If a skin uses transmapped brows, it won't work the same way on V4. V4.1 has brow geometry and a material zone to take the texture, while V4 does not. A dial-spun morph that uses morphs only in V4.1 isn't going to be able to be taken identically by V4 since she'd lack a few of those options; V4 also can't handle the muscle morph or creature morph add on morph packs, which were designed to work with V4.1. Those are the only big differences I can think of.

-D
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It's all fun and games until someone loses an eye texture.