The experiences here seem all to have a common thread, that Autozone can't find their warranty information. I believe they go by phone number and if you changed your number and forgot what it was then they won't be able to find it.
I suggest you simple place the receipt in the glovebox with your owner's manual etc. and then there is no chance for issues. I have never had one but did it as a precaution. I have had several Autozone batteries and their performance has been varied but none of them have ever failed to start my vehicles both large 6 cylinders.
The 2 gold series of the past their top of the line lasted me around 7 years. The midline one I tried one time since I was not going to keep the vehicle for another 7 years failed a load test after 2+ years (I always have AZ check them just before the full replacement period expires and they do it in front of you at your vehicle) Johnson controls makes these and just about everybody's batteries to the specifications requested and or some are just rebranded existing models.
The store in Huntersville, NC is staffed by some people that have been around and I have never had any type of issue with returns etc. I don't think that anybody deleted your information as it would not personally benefit them or the store as per other's comments.
Product or Service Mentioned: Autozone Vehicle Inspection.
Reason of review: Good quality.