The Independent Observer (IO) report, compiled by a nine-strong team and published by world anti-doping agency WADA, said several missed appointments had occurred but blamed confusion over tests relating to the Athlete Biological Passport (ABP).
The ABP programme, making its first appearance at a summer Games, was designed to allow testers to compare blood tests with an athletes' existing blood profile, thereby helping identify unusual patterns or anomalies.
However, its introduction proved problematic.
"The process by which athletes were notified of their selection for such tests can be improved, however," the report said.
"Given that the IOC (International Olympic Committee) deferred to the relevant International Federations (IFs) the responsibility to notify athletes of these tests, athletes were obliged to report for testing at a particular time and place.
"It was observed that in some instances athletes failed to "report" to doping control at the assigned time.
"As no written procedure was available for doping control staff in these situations, no consequences for failing to appear seemed to be enforced by the IOC or relevant IF."
The report recommended that advance notice ABP testing only be carried out in very specific situations, saying that it opened the door for manipulation.
While widely-praising London 2012's anti-doping measures, the report identified a lack of information on the whereabouts of athletes as a potential problem and that national Olympic committees (NOCs) should face sanctions if they fail to provide the relevant information.
"Effective testing can be undermined by a lack of accurate whereabouts information," the report on the July and August Games said.
"The IOC should consider the application of sanctions to ensure that all NOCs provide whereabouts information of their athletes no later than two weeks prior to the start of the period of Olympic Games," it recommended.
The London 2012 anti-doping programme, run by the London 2012 organising committee (LOCOG) and UK Anti-Doping at a high-tech facility north of London, was the most extensive ever seen.
More than 5,064 samples were tested as well as an additional 430 samples collected in conjunction with international federations operating an ABP programme.
A total of eight positive tests were recorded during the London Games, two a result of in-competition testing and six emanating from pre-competition controls.