I had measles as a child (rubella & reg) yet turned up w/ no immunity on work bloodwork. how could that be? gave me mmr vaccine am i know immune?

Yes: Immunity can wane over the yrs. Assuming yr immune system is intact and u are healthy, then an mmr-ii. Would now make you immune.

Mimickry: You did not have a true measles, instead, had some febrile illness with rash. It is not uncommon for the lay people to misinterprete other viral rash as measles.

You are of: An age that you "missed" the measles epidemic of the mid 50s. The definition of "known immune" would be evidence of immunity on blood work, so reimmunization is appropriate.