It's very possible that they did some experiments, and that explains why Kanda is a bastard, although did we see any of those on Lenalee - it was assumed that they did SOME, but the only one I can think of that was shown/described was with the non-Accomodator boy. Lavi could have had Bookman's protection, and Allen and anyone after him haven't been in the Order for very long (~3 months)... although they probably did know what they wanted to by that time. I suppose we'll see more experiments on Allen and Lenalee afterwards.
Hevlaska seems to have been around since the creation of the Order, about a century ago. I think. I recall her saying that.