To start with an obvious point, what's the criteria for a player to be classified as a true Lions 'bolter'? There seems to be at least two camps of players, with the quartet of Marcus Smith, Ben Spencer, Sam Simmonds and Danny Care falling into one - either uncapped or not used by their country during this year's Six Nations, by choice rather than due to injury.
Then you have the players who have burst onto the Test scene in a Lions year having previously been either off the radar or on the fringes, and whose form means they cannot be ignored.
There's even arguably a third group of 'bolters' - injury call-ups to the tour, players who were viewed as likely midweek dirttrackers, who went on to play pivotal roles in the Test series.
With all that in mind, here's how previous bolters have fared on Lions tours from the past 30 years.
Uncapped or underused
Will Greenwood (1997)
There's a reason Marcus Smith's potential call-up has caused such excitement, because no uncapped player has toured with the Lions in 24 years. England head coach Jack Rowell overlooked Greenwood for that year's Five Nations but he was called up by Ian McGeechan for the Lions, becoming a staple of the midweek side.
Greenwood suffered a sickening injury playing against Free State Cheetahs when he almost lost his life, a physical challenge resulting in his head smashing into the floor. He swallowed his tongue and was unconscious for 17 minutes, crediting Lions doctor James Robson for saving his life.
That setback ruled him out of featuring in the Test side for the Lions, and he went on to be capped by England that autumn against Australia at Twickenham.
John Bentley (1997)
Bentley hadn't been capped by England at Test level in rugby union since 1988, switching to rugby league soon after his debut and playing for Leeds and Halifax, before coming back to rugby union in 1996 with Newcastle.
Even so, he was the epitome of a left-field selection by McGeechan and tour manager Fran Cotton in 1997, with Bentley proving to be not just an excellent tourist but also scoring one of the great Lions tries with his slaloming run against the Gauteng Lions. It transformed his tour, with Bentley going on to win two Test caps against the Springboks, his first international matches in rugby union for nine years.
Kyle Sinckler (2017)
Sinckler, then with Harlequins, hadn't made a first Test start for England by the time Warren Gatland selected him to tour with the Lions in New Zealand four years ago. Jamie George was in a similar boat but had been involved with England dating back to the 2015 Rugby World Cup and was part of the 2016 Grand Slam-winning squad and the tour to Australia, whereas Sinckler only came into the fold in the autumn.
Gatland was impressed enough to select Sinckler for all three Tests against the All Blacks off the bench, with the tandem of Tadhg Furlong and Sinckler set to return this summer in South Africa.
The late surgers
Eric Miller (1997)
Miller had won four Test caps by the time he was called up by the Lions, with his Ireland debut coming in a 29-37 defeat at home to Italy on the back of some standout performances for his club Leicester Tigers.
The young back-row's fractured cheekbone in a Lions warm-up fixture against Border in East London looked to have ended his tour early, but he pressed on. Miller was the youngest member of the tour party at the age of 21 and went on to win a Test cap off the bench in that historic second Test victory.
Allan Bateman (1997)
Bateman, like Bentley, had left rugby union in the 1990s to play professionally in rugby league, but crossed back over in 1996. He won a Wales cap against South Africa in the autumn, his first for six years, before three further appearances for Wales followed in the spring, enough to earn him selection on the Lions tour.
Bateman was capped off the bench in the third Test against South Africa and remained in union for the next few years with Richmond and then Northampton, winning the Heineken Cup with the latter.
Jason Robinson (2001)
What an impact. Robinson returned to rugby union in 2000, having had a brief spell with Bath in the mid-1990s, and was used by England three times off the bench in the 2001 Six Nations.
The Lions selectors had seen enough to select him, with Robinson called up for the tour to Australia and scoring a sensational try in the Lions' first Test win, featuring in all three Tests against the world champion Wallabies. As a result of his performances in Australia, Robinson became a mainstay of England's Test side through to the 2003 Rugby World Cup win.
Ollie Smith (2005)
The Leicester centre hadn't started a Test for England since a warm-up fixture prior to the 2003 Rugby World Cup, before missing out on the tournament. But he made two appearances off the bench for England during the 2005 Six Nations, enough for Clive Woodward to include him as part of his squad to tour New Zealand, with Smith going on to start the 2005 warm-up Test against Argentina in Cardiff, paired in midfield with Gordon D'Arcy.
Smith went on the tour to New Zealand despite his father tragically passing away from a heart attack in the same week that he was named in the Lions squad.
Keith Earls (2009)
Injury stopped Earls from featuring in the 2009 Six Nations with Ireland, having first been capped the previous November making one start against Canada at full-back.
His form for Munster and versatility - Earls was selected as a centre, which seems curious now - led to a call-up despite just two Test caps, with Earls honest enough to admit to Off the Ball a couple of years ago that on the plane to South Africa in 2009 he wondered: "What the hell am I doing here with these fellas?" After a rocky first game against the Royal XV, he rebounded to become a staple of the midweek side.
Late call-ups who became pivotal
Martin Johnson (1993)
A future Lions captain on the 1997 and 2001 tours, but in 1993 Johnson had won just a single cap for England against France in that year's Five Nations - when he was a late call-up to replace the injured Wade Dooley - by the time he linked up with the Lions in New Zealand. Johnson again replaced Dooley, who had returned home for his father's funeral.
Johnson was reunited with his England team-mate Martin Bayfield for the second and third Tests against the All Blacks, impressively starting in both games despite his limited experience.
Martin Corry (2001)
Simon Taylor, the ultra-talented but often-injured Scotland No 8, was picked ahead of Corry for the tour to Australia. But knee ligament damage ended Taylor's tour and Corry was flown over from Canada, where he was touring with England, to link up with the Lions squad. He went on to have a monumental impact, starting the first Test in a Lions back row containing Corry, Richard Hill and Scott Quinnell that helped the Lions record a resounding 29-13 victory.
Rob Henderson, the Ireland and Lions centre, later said to The Independent that Graham Henry's decision to drop Corry was "crucial" in the Lions losing the second Test, when Neil Back came into the back row. Corry later returned for the third Test.
Ryan Jones (2005)
Coming off a Grand Slam-winning campaign with Wales, Jones was touring North America with the national side when the call came for him to fly to New Zealand to replace the once again unfortunate Simon Taylor. He joined up with the squad and played in all three Lions Tests against New Zealand, coming off the bench in the first Test before starting the final two.
Jones was another injury call-up in 2009, this time for Stephen Ferris, but his tour only lasted 24 hours after he was ruled out by the Lions medical staff following his arrival in South Africa.
Tom Croft (2009)
Despite a man-of-the-match performance for England in their 2009 Six Nations win over France, Croft was originally left out of the Lions squad for that summer's tour to South Africa.
However Alan Quinlan's ban, after making contact with the eye area of Leinster's Leo Cullen when Quinlan was playing for Munster in the Heineken Cup semi-final, opened the door for Croft to join the squad. He went on to feature in all three Test matches, scoring two tries in the first Test defeat in Durban.
Alex Corbisiero (2013)
Originally not included in the 2013 squad after injury in the spring, Corbisiero was called up to replace Cian Healy during the warm-up matches after the Ireland prop damaged knee ligaments, and Corbisiero went on to have a major impact.
It was Corbisiero's short-range try which kickstarted the Lions' rout of the Australia in the third Test, scoring in the first minute, while he also started in the first Test, proving to be a key addition to the Lions' pack against the Wallabies.