If everything is as you say, there was no reason not to release all data once the Soviet Union was deposed.
I am not following....
“all of the data” would include evidence of an inside coup. They would never reveal that.
“most of the data” would include evidence that direct relatives of people currently in power lied to the American people for years. Sure, they could could claim they were lying to protect the American people but they were lying none the less.
Also, as someone else pointed out. Russia became a target as soon as the USSR fell. Perhaps, the foreign assassination narrative was being kept in the back pocket until such a time where it was feasible and necessary for all out war with Russia. At that time the “limited hangout” could be used to justify that war.