In all my years renting with
Alamo in various cities in US, they have never asked me for a coupon when I use a coupon code. I use the online coupon codes on their wbsite under deals. Nor have they ever questioned my rental discount codes. I give them my DL and they do the paperwork, have me sign and away I go choosing the car I want.
I also think if you prepay there is a no hassle check-in, either with the kiosk or at an expidited desk. I have never prepaid, but I may this time, just to save waiting in line.
Now unless they have changed their rental policies or check-in procedures since last year, no one should have any problems renting a car with any code.
If they changed this and anyone has had a problem lately please let me know.