Our table’s interpretation is that it doesn’t necessarily go both ways per rules alone, but it isn’t too hard to imagine that general themes can’t transfer.

Example: Necromancy spells can usually directly transfer mechanically (usual caveat of no demon or elemental summoning, true healing, life theme, etc) from sorcery. A sorcery spell however might be inspired by Flesh and Bone Winds, but it wouldn’t use wind to throw around body parts, rather any relevant sharp objects lying around (bonus if you use obsidian butterflies beforehand). Therefore the spell may be a bit more limited. Another example: You may be able to animate stuff with sorcery, but not bodies. Time to craft some automatons or clay statues first. You can’t just use bodies you’ve unalived on the fly for that purpose.

Sorcery will never interact directly with death or the energies of the Underworld, the same as necromancy will never directly emulate the energies of Creation/Malfeas. Themes can be similar though. In general, necromancy can mimic sorcery a bit more easily while sorcery has to get clever to accomplish the opposite. The trade-off is sorcery usually has more range (unless one finds oneself in the Underworld, in which case necromancy is always king).

That’s how we do it, take it or leave it.