Sharon A: if it is customarily used then it often passes into the common idiom. Just ask the people at the Collins Co-Build foundation, where they look at all language in its common usage ( corpora). Words and phrases that are used often usually pass from the vernacular into the official. A few years ago the word "like" was officially recognised as a conjunction as well as a verb. i.e: "I was walking down the road,like. When I saw this bloke,like". The possessive 's is another story altogether and is down to incorrect teaching ( or no teaching whatsoever).