Combine pumped milk

I understand you can combine pumped milk from different sections or days (within 3 days) as long as they are same temperature. Fridge milk mix with fridge milk. How about when I warm it up and pour it into the bottle? Can I mix different dates of freezer breast milk bags into same bottle after I warm those 2 storage bags? If so, within what dates between 2 bags? The reason is I have so many 2oz frozen breast milk bags. Wonder if I need to use 2 different bottle to feed or use same bottle