Dipa,

> I have no previous knowledge of placing an apostrophe after the last
> letter
> to signify plurality. All these years of reading and I have never noticed
> this.

Actually, to be precise, it's the plural possessive (genitive) marker. But
you're in good comapny ~ it seems that lots of native English speakers don't
know the different uses of the apostrophe. I cannot tell you how many times
I have seem half-literate writers (especially in the internet) writing
"it's" (= it is) when they mean "its" (= of it) ~ a confusing exception
where the apostrophe is used to denote elision rather than possession.

Best wishes,
Stephen Hodge