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Feelings aside, Part A is always backdated up to six months if enrollment takes place after 65th birth month. It's not optional. The carriers/CMS have just corrected the incorrect Part A effective date you may have put on those applications.hmmm. I'd need to double check, but feels like I have clients who've left group coverage post-65 whose Part A coverage start date did not incur this 6-month retro thing you mention.