The World Anti-Doping Agency (WADA) has confirmed that there may be a lack of "sufficient evidence" needed to impose sanctions upon some Russian athletes identified in the McLaren Report.
In an open letter published yesterday, International Olympic Committee (IOC) director general Christophe de Kepper claimed that WADA admitted that the evidence in "many cases" against Russian athletes may not be strong enough to impose suspensions.
A meeting took place between the Association of International Olympic Winter Sports Federations (AIOWF) and WADA earlier this week to discuss the evidence provided in the McLaren Report.
It was at this meeting that de Kepper claimed WADA made the admission which has now been confirmed by the body.
"Unfortunately, many samples were disposed of by the Moscow laboratory, which means that they could not be re-analysed," a WADA statement read.
"As well, requests to Russian authorities by Professor McLaren for additional evidence went unanswered.
"Together, this means that there simply may not be sufficient evidence required to sanction some of the individual athletes identified in the McLaren Report.
"The anti-doping community must be clear on what it can and cannot achieve based on the evidence that Professor Richard McLaren was able to uncover."
De Kepper also said in his letter that WADA explained to International Federations (IF) that the translations used by the McLaren Report were not adequate and that it was obtaining official translations of some of the texts.
Proving athletes had knowledge that their samples were being tampered with is thought to be a stumbling block in many cases.
This news is being welcomed in Russia as a suggestion that McLaren's wider conclusions are flawed.
"I can only say that we will continue our consistent work to restore compliance with the code of the Russian Anti-Doping Agency and WADA," Russian Sports Minister Pavel Kolobkov told Ria Novosti.
"Our federation will continue to work with international federations.
"We are absolutely open and willing to cooperate, and I hope that these findings will be another step in the right direction."
IFs and the IOC are continuing to analyse the WADA-commissioned report before taking action against athletes and officials involved, along with the entire Russian doping apparatus.
Evidence showed that doping samples submitted by up to 1,000 sportsmen and women had been manipulated across Summer, Winter, non-Olympic and Paralympic sport.
Disciplinary proceedings have so far been opened against 28 Russians alleged to have been part of this programme at the Sochi 2014 Winter Olympic Games.
Previous concerns about the data were raised by IFs last year when the first part of the report was released.
Several world governing bodies claimed to be unable to find conclusive evidence of involvement regarding athletes supposedly implicated.
De Kepper also claimed in his letter that the IOC is encouraging WADA and Russia to re-establish state-of-the-art anti-doping institutions in the country and ask that athletes from the country "undergo anti-doping tests with higher benchmarks than for athletes from other countries".