I also wonder why the homunculi's master didn't create them all at once to replace the old ones.
I mean, in ep35 Envy says that the master could do a new greed like if it was nothing for him/her (no body price to pay ??), so why this person waited to get a new sloth,lust,wrath (in the case of wrath it was wise to let him get ed's body part to êrform alchemy
)
in the manga the homunculi are truely the Father's creations, he probably needs to a lot of researches to design better homunculi, but I feel that the anime's "spontaneous generation theory" added by bones just doesn't fit together with this.