I have done a number of these. I count the sf as above grade GLA. Never had problem.
We have a lot of these here as well. It's all over the map as to how the county assessors and realtors call the spaces around here. Personally, I've gone back and forth over how best to call these things over the years and have decided it's best to take them on a case by case basis.
I've never ran into any real problems calling the space however I wish to call it on a report, other than occasionally an underwriter will want more explanation or maybe ask I move this or that to another line on the report.
Ultimately, I think it comes down to a matter of form and function. Technically, the room I am typing this from within my own home is "below grade". Or, at least the back few feet of it, as my house it built into a hill. The front door is on the lower level which leads straight back into this room which is in the hill. Above me is the kitchen which has a back door that leads to a patio that is on the hill. The form and function of the home is one living area. You have no sense whatsoever that the front door leads to a "basement" or that at any time do you feel like you're sitting "below grade". But my home looks like a two story home from the front, and like a one story home from the back.
The county calls it all GLA (except for a small 168 sf utility room that is unfinished and also below grade. It calls THAT the 'basement' even though it is not more 'below grade' than is my office space.) The appraisers that have appraised this home over the years all call it all above grade GLA.
If I were appraising the house and some underwriter wanted to get technical and ask me to put the hundred square feet or so of this house that is below grade on another line, I could do that. But it'd just be a reporting function that would create an uglier report with unnecessary adjustments, IMO. I'd still be comparing it other houses of the same size without anything below grade because the fact that some of it is below grade does nothing to change the value.
The biggest annoyance I run into with underwriters on this stuff seems to be what to do about bedrooms and baths. If I've got a house with a finished basement that functions as part of the GLA with a combined 4 bedroom/3 bath count, then I'm going to be looking for homes with similar living space and room count. If I can find one with a similar finished basement, great. But if not, I'll compare to homes with the same GLA and room count all above grade because that's what the buyers in the market would do.
So if I separate out the below grade stuff on another line, the underwriters get upset that now I've maybe got across-the-board adjustments for room count on both the above - grade and below -grade lines. Even though they add up and cancel each other out. But put it all on one line, and now they are upset that I didn't separate out the below -grade stuff.
So it's a lose/lose sometimes in that regard.