Clear to one is murky to another!
"We" may know the answers, but the rest of the world does not.
GBA = 2,000 sf (I have seen garage area included in GBA; it should not be.)
GLA = 1,000 sf (There is no difference between "industry standard" and FNMA guideline)
Finished living area = 1,500 sf
Area under roof = "It depends." Some will say 1,000 sf, some will say 1,400 sf, some will say 1,600 sf. I say 1,600 sf...so do most of the agents around here and so does the county appraiser. Air-conditioned area under roof is a different matter. Again, some will say 1,000 sf, some will say 1,500 sf, some will say 2,000 sf. I say its almost time for a beer!
For SFR, one reports GLA.
The "trick" question...FNMA does not state one "must" report GLA in a certain method. The "guidelines" suggest a way it should be reported, but they also recognize there may be property-specific circumstances where it may be appropriate to digress from the suggested guidelines.
For 2-4 residential properties, GBA is reported. GBA includes below grade area. Have a split foyer that has been legally and physically divided into a duplex and is leased out? That's a 2-4 family property. The whole above grade GLA/basement finish question is moot.
But we all knew this already...basically my point is that different segments of the industry and different geographical areas will describe the same property feature differently.
Now, what do you call a split foyer that has a lower level not just totally above grade, but on a crawlspace to boot?
"Dumb" (but real...and reported as a split foyer with a lower level "below" grade for comparison purposes. You can put slicks on a dumptruck, but that doesn't make it a race car.)