Sorry, I just don't buy that the Borg who are assimialted look different to the Borg who are grown in maturation chambers. There's no reason to believe it apart from the difference in appearance between the pre-FC and post-FC Borg.
And even then, the idea is shot down by the fact that the FC style Borg are the type that has been assimilated as an adult (remember Ensign Lynch?), so that means that if the other look for the Borg is the "grown in a maturation chamber" kind, why did Locutus look like that?
We've seen an adult assimilated and look like the old style, and we've seen an adult assimilated and look like the new style. So I don't see how there's any justification for it.