I'd have to check em, it was just a guess, but I have two airs from the last decade (2009 and 2015 I think) with their original operating systems and I think one is around 10.4 and the other 10.10ish.
Maybe I misunderstood your question... I never updated the OS on either of them. Or on any Mac I've owned since the mid 90s.
> took two airs for almost a decade from 10.4 to 10.10 or something
Iām curious, did macOS 10.4->10.10 not constitute an OS update? Or was this a time when you applied your rule differently?