The thing to consider with breastmilk- is the milk fat calories change constantly for the baby depending on how many times they nurse etc...
so your source may have different values depending on who else they are nursing.
Also in tack proteins pass through breast milk- again this varies upon the mother (defeats the purpose of most EN) could irrate things
One last thing breast milk is very easily disgusted (hence infant usually eat every 2 hours) to use as EN that would mean ALOT of bresatmilk to be supplied by one person. Most milk banks would need a script.