"It's not too common to have the "classic" form of DID in which there is a change in alters(personalities) with amnesia between them."

To even meet the criteria of having a dissociative identity disorder or Multiple Personality Disorder as it was formerly called, one MUST have amnesia between the states of being (personalities).

Therefore if it wasn't or isn't common to have the alters (personalities) switch WITHIOUT the amensia between the personalities, then it would be impossible to be dissocative idientities in the first place, and so on Allen. Just my 2 cents worth.