Stage 2 ("widely shunned"): The form spreads to a significant fraction of the language community but remains unacceptable in standard usage (e.g.: *"real trooper" for "real trouper"). Have seen this. It’s not uncommon. Hoping it will remain at Stage 2.
Stage 3 ("widespread but . . ."): The form becomes commonplace even among many well-educated people but is still avoided in careful usage (e.g.: "usage" misused for "use"). Sorry, folks, but I have been guilty of this myself a few times, but it is an affectation.
Stage 4 ("ubiquitous but . . ."): The form becomes virtually universal but is opposed on cogent grounds by a few linguistic stalwarts (die-hard snoots) (e.g.: *"is comprised of" for "comprises"). I am a stickler about this, but you do see it in some respected publications. Remember, the whole comprises the parts. So, “The team comprises 24 distinct personalities.”
Stage 5 ("fully accepted"): The form is universally accepted (not counting pseudo-snoot eccentrics) (e.g.: "daylight-savings time" for "daylight-saving time"). I made a point of this in an early column, pointing out that the phrase had nothing to do with money – “savings” – so it is daylight-saving time. And, prescriptivist that I am, I’m sticking to that. And, incidentally, I resent the “pseudo-snoot eccentric” label.