BFFL's

Just to be clear, the apostrophe in the title has no semantic content; I'm pluralizing BFFL (according to MLA style, which is what I usually use). The reference, for those who aren't aware, is to a recent commercial that I keep seeing everywhere concerning mothers and daughters recollecting about barbie dolls. At one point the daughter in the commercial describes two dolls as "BFFL's -- best friend for lifes". This strikes me as odd, as I'm guessing it does many people. The oddness here comes from the scope of plural morphology. While possessive morphology attaches to a NP ("a friend of mine's cat", not "a friend's of mine cat"), plural morphology attaches to the head N ("friends of mine", not "friend of mines"). The reason behind this NP pluralization could be for two reasons: (1) reanalysis of the plural morpheme as attaching to a NP rather than a N, or (2) reanalysis of "best friend for life" as a single noun rather than a NP. My bet would be on (2), since the acronym BFFL is a single noun for all intents and purposes, which could in turn lead to an analysis of the entire phrase "best friend for life" as a single noun. Something similar has happened with "passer-by" and "mother-in-law"; many people would pluralize these as "passer-bys" and "mother-in-laws" because these set phrases have been reanalyzed as simple nouns. Others (myself included) still treat these as noun phrases, and thus pluralize them as "passers-by" and "mothers-in-law".