I am sure this question has been asked & answered many times over, but I did not see it in a search.

Over the years & oil changes i have wound up with all sorts of miscellaneous partial quarters of oils sitting around in my garage. 15w50, 20w50, synthetic, dino, etc. All of this has me wondering... is it safe to use different oils to top off so i can get rid of these? Like say is 15w50 safe to add to what is essentially a 10w40 oil change? what about adding a dino to a synthetic?