I just updated to Glyphs Version 2.5 (1131) and I noticed something changed in the weight classes for Thin, which used to be 250 and now is 100 and Extra Light and Ultra Light, which used to be 250 and now are 200. FDK Compare Family is flagging the Thin weight (I didn’t have any Extra or Ultra Lights in my test file) :
Single Face Test 9: Check that no OS/2.usWeightClass is less than 250
Error: OS/2.usWeightClass is 100 for Font Test-Thin
This may cause the font glyphs to be smear-bolded under Windows 2000.
The issue with Windows was already mentioned in this thread: Font Menu Order, Thin <> Extralight
Is it now safe to keep the weightClass at 100 or is it better to change it back to 250 with weightClass custom parameter even if we are 18 years away from Windows 2000?