Many have had fire stops put in during renovations, the multifamily I own drilling through the masonry was quite a bitch to run a new wire. Not that uncommon to be able to shine a flashlight up from the basement to the attic though. It sounds like you are a tradesman so I'm sure you've seen lots of walls but a lot of the multi-families I've gone into are basically maintained only to the point of passing section 8 standards and the slumlord landlords don't hire proper pros when doing work.