World Anti-Doping Agency officials say "points still need to be ironed out" before they are given full access to a suspended Moscow anti-doping laboratory.
Wada ended a three-year suspension of Russia in September, following a scandal over state-sponsored doping.
But a key condition was that access be given to the Moscow lab and its data.
Wada says it is aiming to carry out a "full technical mission" at the laboratory by the end of the year.
"We had open and productive meetings with the Russian public authorities," said Wada's science director Dr Olivier Rabin.
"Progress is being made but some points still need to be ironed out before we can proceed with the technical visit.
"For Wada, the sooner we can gain full access to the laboratory, the better. Clearly, there is a huge volume of data contained within it and we want to start analysing it as soon as possible."
He added the data at the laboratory was the "missing piece of the puzzle" regarding the country's doping scandal, which led to its athletes being banned from international competition.
"Once the data has been fully assessed and verified to be authentic, we would be in a position to assert anti-doping rule violations against those athletes who cheated and to exonerate other athletes," added Rabin.
The decision to lift the suspension of Russia's anti-doping agency provoked an outcry and was even described as "the greatest treachery against clean athletes".
Wada president Sir Craig Reedie defended the move and said the reinstatement was "subject to strict conditions".
How the scandal unfolded
- December 2014: As many as 99% of Russian athletes are guilty of doping, a German TV documentary alleges.
- November 2015: A Wada commission publishes an independent report alleging widespread corruption, amounting to state-sponsored doping in Russian track and field athletics. Rusada is declared non-compliant.
- May 2016: Former Moscow anti-doping laboratory boss Grigory Rodchenkov, who has turned whistleblower, says dozens of Russian athletes at the 2014 Winter Olympics in Sochi had cheated.
- July 2016: Russia operated a state-sponsored doping programme for four years across the "vast majority" of summer and winter Olympic sports, says a report from Professor Richard McLaren.
- August 2016: International Olympic Committee (IOC) decides against imposing a blanket ban on Russian athletes at the 2016 Olympics in Rio. Individual sporting federations rule instead, with 271 Russians competing.
- December 2016: Wada publishes the second part of the McLaren report which says more than 1,000 Russian athletes benefited from doping.
- January 2017: Rusada and Russian sport authorities given list of criteria to achieve before winning back recognition.
- March 2017: Wada says Russia's anti-doping reforms are not happening quickly enough.
- February 2018: Russia are banned from competing at 2018 Winter Olympics in South Korea by the IOC, but 169 athletes who prove they are clean allowed to compete under a neutral flag.
- May 2018: Wada writes to Rusada offering 'compromise' solution.
- September 2018: News of the compromise, revealed by the BBC, prompts fury from athletes and doping bodies.