When polyester resin is past its shelf life what happens?

My supplier of surfboard resin warned me about the shelf life of the
typical slighly greenish surfboard resin. Also, I have read that
catalyst or MEKP has an even short lifespan.

I have had a can of resin and some catalyst stored in my upper Midwest
backyard shed since last summer. It went through a winter with many
subfreezing days. I have read that once a can of resin is in freezing
cold that it will never be the same.

The stuff looks fine. Yesterday, I made a batch. It cured normally.
I have a 3/8" thick disk now. I cannot break it with my hands.

All I have to say is: huh?