When to use the stash?

Hi everyone. I’ve been EP-ing since birth and now have some supply stashed away starting from Apr 15th.

From guidelines it seems like breastmilk stored at -20 deg. C can last for about 3 months. My question is, if I currently have enough for baby to drink daily, when should I use the frozen breastmilk to make sure the stash doesn’t go bad? Do I supplement the fresh breastmilk with the frozen a couple times a day?

Thank you!