Pull the file and look in the title report for that information. I can provide you with a couple of links mentioned by the last poster, but I think it might put you back where you are now. One other option is to call your regulator directly. I have a strong relationship with mine and call when I'm in a pinch.
It sounds to me like the apartments were an after thought(Basement) to a commercial property but you know about them now so you still have to deal with the issue of course.
http://www.ffiec.gov/cra/guide.htmhttp://www.dallasfed.org/htm/pubs/pdfs/ca/craloan.pdfIt feels like commercial to me still, it's two basement units, but it's 50/50 sq ft. I'm coming close to changing my mind to HMDA too.

Get the zoning from the file and if your regulator isn't available I'd be happy to call mine