Tell us; What did you do before ANSI??
I have used ANSI for a Long Time. The difference between then and now is simple. Then I was not fenced in to specific/hard stop ways of measuring. For example: all Condo's, and Townhome style condos/SFR attached/semi-detached I measured interior paint to paint., 1st and 2nd floor. Octagon and Circle shape house ? First they are rare in my Hicksville town and mostly rural county. Easy Peasy Geometry is your friend. Back then then most common in my area are ranch style homes two pulls of the tape.
What I did not do is obsess over precision 1/10 or 1/12 a foot. I started with whatever exterior was the longest or easiest to measure.
One of the areas that we seem to be bringing up quite a bit are discussions about Above and Below Grade Finished area. 1st: Basements are basements. Above and below grade finished space is just what it means. Its not a basement per se. What is a common response: The market recognizes this area as finished space, Ok! What is not talked about is Fit N Finish of those separate areas.
Stop Obsessing! just do the best you can in spite of your Declaration that you Followed ANSI !!!! Rule #1 Use Common Sense. What often looks great on paper requires ignoring Real Life!