Hmm, there r two schools of thoughts. My colleague who is a mom of 4 kids, said tt thawed ebm, even if leftover from a previous feed, u can still put back in the fridge n used within 24hrs. So far her kids all ok n didnt develop any diahorea from drinking leftover thawed ebm. I have also read online tt bm has alot of anti bacterial properties, n an experiment conducted showed tt bm tt has been partially consumed, did not have any bacterial in it even after 24 hrs.
I suppose, it's yr own comfort level whether u want to err on the safe side or whether u want to save every drop of ebm. Just like whether or not to sterilise pump after every use..