To my knowledge I have not seen a single lender, ever, use EX FICO 3.
I find the idea of USAA using it laughably absurd, 99% sure they're on FICO 8 and have been for years but I haven't been keeping track but there was zero reason to go backwards.
Honestly EX FICO 3 is the score that everyone forgot; the GSE's didn't move off EX FICO 2 and many lenders especially Credit Unions have followed their lead, and the rest of the industry (auto / credit card) hopped straight to FICO 8 or the corresponding AU / BC industry option for that generation of scores. Every lender that I have seen on this forum, or worked at (there's been a few) has followed that pattern.
As for the personal loan purveyors, those all rose to prominence well after FICO 8's release and after most of the major credit card and auto lenders had already adopted scores based on that model and to my knowledge they all followed suit too. EX hasn't withdrawn it so maybe there are some out there which use it, but it's not the 99.99% of the market and there may be more 9's to the right of that decimal point too.
I occasionally look at it for giggles but honestly the only 3 scores I care about for EX are FICO 2, FICO 8, FICO 9 in that order.
That said assuming files are identical and have derogatory information, the best score I have found for estimating EX FICO 3 is EQ FICO 5; both of those much more heavily penalize negative information than any of the other scores (including the same generation TU FICO 4) and have been close to in line for me with very minor differences between those bureaus for me over the years I was tracking in the dirty scorecards. Once clean EX FICO 3 tracked differently as EQ FICO 5 shot the moon.
