OK, two different things going on:
1. Will Cap One agree to do a product change, and if so, will they show the age of the new card as that of the orignal(s)? --depends on the company. There are a lot of Cap One people here, and you'll hear from them PDQ, I'm sure.
2. What will happen to my length of credit history if they don't keep the same opening date on the new card? --All credit accounts remain on your reports for 10 years after closing. If you had any negatives on them, they will show for 7 years from the time that they happened and then fall off, leaving a minimum of three more years of clean history showing. If the new card reports a current opening date, instead of the old one, your average age of accounts will drop, depending on the age and number of your other accounts.
FICO scoring looks at both age of oldest account and average age. So on oldest age, nothing would change; on average age, it might drop slightly or a lot, depending on how many other accounts you have and how new they are.
* Credit is a wonderful servant, but a terrible master. * Who's the boss --you or your credit?
FICO's: EQ 781 - TU 793 - EX 779 (from PSECU) - Done credit hunting; having fun with credit gardening. - EQ 590 on 5/14/2007