If it looks good, it's good. I'm pretty sure bees make stuff to last like that.
Unused toilet wax been baking out in my hot Dallas garage for 2 summers now (and 2 winters but our winters are pretty lame). Is it OK to use?
Yes. It will "BEE" aright.
Have you checked it see if has melted during the hot summers?
Licensed residential and commercial plumber
I guess not since it still looks like its original shape.
If it hasn't melted or radically distorted, it should be fine. It may be a bit harder than a newly boxed one, but it should still function properly. Let it come up to room temp before using if it's cold in the garage.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014