Mr Red: all your wordses are already pluralses except for octopustuleseses's, of which the plural is squid.

I don't like foreign plurals creeping into the language; it's already complicated enough, and words should be naturalised as soon as possible. So the plural of stadium is stadiums, not stadia, which are ancient Greek kilometres. The Greeks trained in gymnasia, but we (you I should say) go to gymnasiums, unless you do it in the nude. And as for data- in 30 years in electronics, I've never heard the word 'datum' except to mean a fixed reference point for measurements. Even one bit of data is data.

Anyone:
Write me a sentence in which the omission of the possessive apostrophe causes ambiguity. I bet it's a badly framed sentence that would be difficult to construe anyway.

The boys trousers pockets holes were caused by the girls frolicking.

Any problem?