Sorry to resurrect an older thread, but I had a slightly different experience with this recently. Within the past six months, my wife had two Alamo rentals and I had one, all booked through Costco. We forgot to provide our Southwest RR numbers, at the time of pickup, in each case. So a few months ago, I mailed in the rental agreement copy to the address that
used to appear on their site
here. Now, there is no mention of a mailing address, only a phone number.
Nothing ever happened with the points, so I called Alamo today to inquire. The rep was able to add my wife's RR account to one of the rentals, but said there would be an additional airport surcharge of $0.75/day with $7.50 max. I said that was fine since the value of miles (600) was presumably higher. However, for the other two past rentals, she was not able to add the RR account. In one case, she said it was because one was a one day rental (from Oakland, CA), and in the other case, it was rejected due to the rate.
It's a little frustrating since it runs counter to my previous experience with other rental car companies, where I just mail in the letter, and the points show up (with no extra charge). I'm wondering if my experience is typical? I also wonder if the outcome would have been different if only I'd remembered to add the numbers when picking up.