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American Greetings made a set of Muppet greeting cards in 1992 and 1993, and another set from 2005 - 2007.
1992/1993
"...In fact, once a year per person is my limit."
"...No cake until you eat all the candles!"
"...But enough about me -- happy birthday to you!"
"Sometimes a good aaarrrgh can help you get through the day."
"And, if it isn't, call the police, 'cause there's a naked stranger standing where your mirror should be!"
"Doesn't that make your day?"
"...is the person who receives it!"
"I didn't think so!"
"So I'll just have to put them into kisses!"
"...Moi!"
"They were all married! Have a happy birthday anyway!"
2005
2006
2007
(blank)
"...I'd much rather dance beak to beak. Happy Valentine's Day!"
"Cracking them up. Get it? ...cracking them up? Geez, tough crowd. Happy Easter."
"...but could you at least skip the ham?"
"...I'm partial to green. Happy Easter."
(blank)
"You shouldn't have! (... but who am I to stop you from being generous?)"
"Just a shout out to a good friend."
"Happy Borkday"
2008
"I scream and cake! Happy Birthday"
"It's your birthday - make a fashion statement."