Yes, this is exactly how it works, a mothballed tank is taken from the warehouse, the re-mothballing procedure is carried out and the tank is ready to fight. Ukrainian fighters of the defense are similarly armed with Soviet-made Kalashnikovs, they are new in factory lubrication, as part of the Ukrainian legacy from the USSR. Old Soviet tanks played an important role in the military doctrine of the USSR, providing the ability to strike with a mechanized tank column within 48 hours anywhere in the Eurasian continent. The current military doctrine of Russia is more progressive and less relies on the brute force of tank divisions, but the tanks themselves have not gone away. That's where they came in handy.