it really depends on what kind of feel you are going for.
For example, Fallout uses things like Nuka-Cola and Sunset Sasparilla in place of coke and root beer, but they also use actual places like "New Vegas" built on top of old Las Vegas.
The feeling that is created in this world with those products is more comical, but that's not necessarily needed. What is important is that in these cases it makes the world have more of it's own "personality" Where if you were say taking the movie Cloverfield, using coke would be more appropriate because it's supposed to be directly related to real life. both are alternate realities and both methods of writing have their merit, the choice really belongs to the writer, however I can say this, when you make things your own, and you do it to a point where it's really believable, it is a lot more work, but your readers also appreciate it a lot more too because it gives them more escapism. You can also offer the generic route as mentioned by Dauph. And I'd argue not everyone knows what a '63 mustang, that's a connection the reader needs to make. Also, the free advertising route can even be played for laughs as is done in the comedy "wayne's world" or it can be done simply as an off hand suggestion to the reader. All in all it really comes down to writer preference. If planning on having something published though, the more stuff you don't refer to the better due to how people get uppity over nonsense.
I would say just bring it up, keeping the guidelines of MW posting in mind (be excellent to each other, etc.). if you don't it looks sloppy to other readers. If you're talking about the collabo being worked on at present in the writers guild, i would say it's not overstepping to quite the previous wrong post, point out the inconsistency and then redraft the same post with corrections so it makes sense. Just make sure you're keeping corrections to a minimum.
For example, although I didn't explicitly say so, I assumed the female character lived in a NYC apartment. Then you said she had a basement. But since it wasn't clarified we have a new paradigm to work with.
I think any mature person would take direct criticism of that nature and be cool with it. If they don't, well, you can't please everyone.