Best Banks to use for Authorized User Credit Piggybacking

[Anonymous]

I am working with my girlfriend to improve her credit. I am going to add her as an authorized user to some of my older cards to give her credit report a boost. I am trying to figure out which banks report the date the authorized user was added to the account versus the original date that I opened the card. 

I have cards with Chase, Citi, Amex, Discover, Wells Fargo, Elan, Capital One, and US Bank.

Based on my research so far, Citi reports the date I opened the card whereas Amex reports the date the authorized user gets added to the account. How about the remaining banks, what date do they report?

P.S. (I carefully manage my credit utilization and have never missed a payment so there shouldn't be any concerns about those factors)

Thanks!

[PutThatMoneyOnTheTable]

AFAIK Capital one also reports the date the card was originally opened and not the date the AU was added.

[gdale6]

Cap-1

[Anonymous]

Thanks for the responses thus far, does anyone else have knowledge of the other banks (Discover, Wells Fargo, Elan, and US Bank)?

[Anonymous]

Bump

[K-in-Boston]

Chase, Citi, Discover, and Capital One all definitely report the entire account history.  Amex uses the date the AU was added as the account opening date.  Not sure on Wells Fargo, Elan, or US Bank, but I think Amex is the only one that works that way (which was changed when they stopped backdating new accounts for existing cardholders to the first year they were a member back in 2015).

[Anonymous]

OK thanks, that's very helpful