My wife's first was an Amex Plat as well.
It wasn't really a credit card, (only could be used in gap, not anywhere else.)
Amex Blue Sky
Cap1 plat. Started at $500, later went up to $750!
$750 - wow!until I started thinking about MS I hadn't even noticed that Chase raised my freedom CL from $500 to $700.But my spouse's (only) credit card has a $300 CL! Don't worry - even though we're only married 2 weeks we already have a sapphire preferred coming in the mail...
Funny thing is, I now have cards with $20k-$30k cl, yet they never raised that card again passed the $750.