I actually own "Strategic Nuclear Targeting" edited by Desmond Ball. This is a fairly comprehensive and as far as I know unique book on this arcane subject.
If the contributors the book know their stuff it seems very unlikely that cities like Brasilia would be hit.
After all, the intent of Soviet targeteers was to destroy NATO. I can't see them allocating warheads to places like Brasilia at the risk of omitting really important targets elsewhere, and given the so-so reliability of Soviet delivery systems they would IMO plaster the really vital targets at the expense of marginal places.
After all, following this logic to the nth degree, you would be hitting every concentration of human beings in the world. Surely the targeteers had their priorities spelt out?
Now in the months following an Exchange, when all weapons were free and there was no Command Authority left, yes I can imagine individual boomer commanders on both sides picking their targets of choice, which could be anywhere.