Adding AU to Cap 1 account - address/backdating questions

[masscredit]

I'd like to add a very close friend to one of my cards as an AU.  She had a rough period in life then went years with no credit so she's starting from the bottom. She really needed a new car so she was able to get financed through Cap 1 (17% - ouch!!!). A month later she got an unsecured card from them with a $500 SL. Scores are in the mid-500s and AAoA is 2 months.  The goal is to get her EQ04 score to 680 so she can refi the car with DCU. That will get her their best rate. Without that she's going to pay close to $10K in interest. 

My oldest account just happens to be with Cap1. It will be 6 years old in October. Combining the history of that card with hers will bump her AAoA to 3 years.  From what I've read that might be worth 15-30 points.   My two questions are -

Cap 1 definately backdates AUs right?  I read they do but just want to make sure.

We don't have the same address. Will that matter?

Thanks!

[Gmood1]

It won't matter. She'll still get your credit history. Neither my brother, sister or oldest daughter share the same address. My Cap One is on all of their reports . Cap One is also my oldest line.

[K-in-Boston]

In 2016 CapOne backdated me to 1999 as AU on my wife's card and her to 2004 as AU on my card.  I am not aware of any change in that policy.

[simplynoir]

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@K-in-Boston wrote:

In 2016 CapOne backdated me to 1999 as AU on my wife's card and her to 2004 as AU on my card.  I am not aware of any change in that policy.

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There isn't and I did it very recently. Added my brother to my 13 yr old CapOne in May and two younger sisters in June as well and they reported as they should the following month.

[masscredit]

What kind of gain did they see from being added as an AU?

[Gmood1]

The results varied per individual and depending what was already in their files.
GF's scores jumped around 40 points. After the Alliant SSL last AUG her scores were solidly in the 600s. She still has some old active baddies and collections. Her scores were in the low to mid 500s. She's now in the mid to upper 600s. I added her roughly 18 months ago.

Step daughter didn't have any credit..not even a score 15 months ago. All of her FICO 8 scores are in the 765 to 780 range with 1 year of credit history.
I added her to several cards that didn't back date. If I'd have put her on Capitol One, she'd probably be at 800. Lol
She financed her first vehicle a couple months ago..got the best rate through Navy.

Oldest daughter had some lates and missed payments. She was also in the mid 500s at the beginning. I added her last summer. Last we talked , she told me she was in the upper 600s. Financed her first vehicle through Navy with the best rate earlier this year.
I added her to the Capital One card .