OK, so I'll repeat all of these answers since you've been replying without following along apparently.
Smoke smell was centered in the kitchen/laundry. When it wasn't at it's worst, you could track the source of the smell to around the stove and near the HVAC in the laundry room. How it was getting in, I don't know, I'm not a home builder or contractor. I am very handy and typically handle nearly everything at my house myself, but that apartment wasn't my home. I'm not spending my time or money to fix something that I don't own. That's just silly for you to even suggest (you did this in an earlier reply).
I thought the following went without saying, but I guess not. There wasn't a wall of smoke in the sense that I could see smoke like it was a fire or something. The wall of smoke was referring to the smell.
Again, the maintenance guys hypothesized that the smoke was somehow getting into my apartment through cracks around piping under the sink, around the HVAC, etc so they used the expanding foam on those areas. TO NO AVAIL.
I also have never heard of smoke going between walls, but smoke is smoke. Just like water, if there are no barriers to entry, it will find a way. But, again, I don't think it was going between the walls or spaces around piping (clearly because their solution did not fix it), but somehow getting in through the venting or something.
And to repeat myself again (I'm not sure why this is hard to comprehend), we moved in to the apartment at the end of July. No smoke smell at all until the weather got colder (meaning the smokers moved from smoking on their balcony to inside their apartment). I suppose it could've been new tenants, but considering the maintenance guy said he knew who it was, I doubt it.