Syntax mistake—not grammar

It’s*

$5 isn’t a *lot

Think of the phrase: about music. “90’s music” would imply music from specifically 90 (probably 1990 where we assume the writer was lazy about the initial apostrophe)—possessive form. “’90s music” uses ’90s as an adjective for the entire decade—and with the preceeding apostrophe makes it clearer 19 is omitted. 1 year versus 10 years as a big difference. Using an apostrophe in the right place clearly removes the ambiguity.

It was an error. It happens, and too many people do it so next time maybe you won’t with a good habit being formed.

for Mobile OS’s

for mobile OSs*

One man’s pedentry is another man’s pet peeve. This is a syntactic error that isn’t just a typo but a misunderstanding of the mechanics of apostrophes.

Really. Apostrophes are used for possession & contractions (not making words plural). In this case, you are omitting the 19 from the decade starting at 1990. What is plural is the years inside that decade, meaning the 10s place. All to say, it is 100% ’90s*.

in the late ’90s*