31th or 31st
101th or 101st
1001th or 1001st
Can I also use that way everywhere in the same way (for example, ordinal numbers in math)?
I think the 101st Airborne Division (U.S. Army infantry division trained for air assault) is a defining case for “standard” usage.
Having said that, in light of 6800 written instances of 101th I can’t say the alternative is “wrong”.