I'd be guessing that the more recently manufactured Solos have the Rev B - but that doesn't mean that you'll get one of those if you order/buy a Solo today.
My 1st B&H Solo, Rev B. 2 weeks later, my 2nd B&H Solo, Rev A. Haven't checked my 3rd from Prime Day yet. It is what it is...
I must cross my fingers then...
Luckily with 3DR Shield even Rev A works well... so it is not a real issue....