I have no idea where the author got this... this was maybe(!) true for very high ranking party members, but for normal people, there was no inheritance and trading, and the use was the same as with any other rental apartment. Also maybe only in what was left of yugoslavia in 1991 and then turned into 'serbia and montenegro'. If you died, the apartment went back to the state. To trade it (move elsewhere) you needed a good reason (usually, more kids or more rarely a new job).
I was born in yugoslavia and lived here/there until the fail, and now still live in the same city, just in a new country. My parents got a social apartment, I got born and they got another apartment and moved (1->2 bedroom apartment). They couldn't get a bigger one before, because 2 people meant 1 bedroom apartment, 3 people, two bedroom one. They couldn't even choose the floor (noone wanted the ground level or top level ones). No trading, no inheritance, no ownership until 1991 and the jazbinsek law, where every renter could buy off the apartment from the government.
Or did she live in another apartment, and when he died, she got his, better(?) apartment?
If someone dies and you get to stay in an apartment, that's not inheritance, just continuing to rent that apartment.
https://www.tandfonline.com/doi/full/10.1080/02757206.2017.1...