How else do you think the Soviet factory managers could meet their quotas for the month? "Yes, we shipped out 47 T-34s last month, and exceeded our production quota of 45.", never mind that 22 of them were repairs or overhauls. The problem is that math is apolitical, but HOW and WHAT you count is most certainly politically determined.
Consider modern US inflation figures, which include several items with prices that are government regulated. The final numbers are whatever the government wants them to be, and "accounting adjustments" regularly prevent the discrepancies from becoming too obvious over the longer term. It was probably in the interests of quite a few people in the Soviet Union to count tanks in that manner, and trying to make any sense of it decades later could be a challenge.
As an example of "creative accounting" at its finest, the major purpose of a military parade was to demonstrate for the reviewer that the proper number of equipped and trained troops was indeed present, as stipulated in the contract or decree. It was often in the interest of the officers, generally in conspiracy with the supply clerks, to run the unit a few bodies "light", yet claim them and pocket the difference in pay and sell the surplus supplies. It was in the interest of the government to insure that they were getting what they paid for, occasionally sending inspectors or senior officers to review the troops without notice. People got rich on the discrepancies, or got arrested.