Has anyone had issues with a multi-family not being zoned correctly?

[John Hanley]

I have been looking at some 6 unit properties in MA and NH and I am finding that they might be listed as a 6 unit but after doing research I find that it is zoned as a 5 unit. All of the units appear to be up to code so I'm not sure why they aren't officially listed as a 6 unit.
Does anyone have any suggestions on what to do when dealing with these types of issues.