Whatever happened to a noun ending in ‘s’ simply ending in the apostrophe to signify possession?
‘Thomas’ eyes are blue’.
Add a superfluous ‘s’ to balance out all the ignoramuses who think plurals get an apostrophe. Can’t risk a distortion of the gravitational flux.
s’ is normally used to convey plural possessive. So your example implies there are multiple ‘Thoma’, all of whom have blue eyes.
A plural noun is made possessive by an apostrophe.
You are confusing the final “s” in “Christmas” as a pluralizing “s” rather than its being part of the noun.
The correct way to pluralize a singular noun ending in “s” is to add an apostrophe and an “s.”
I call this “Jesus’s Rule.”