Many vertex lights in custom surface shader lighting

Hey! Got a shader issue I haven't been able to figure out, thought maybe y'all could! So I've got a scene with multiple point light that are set to "Not important" render mode, which as I've understood it should make them vertex lights. Having many of them works fine with a shader that uses the Standard lighting model, but as soon as I make my own lighting function (for instance the SimpleLambert from unity's shader examples) only the one brightest light of all the vertex lights affects any one model at a time. Has anyone figured out what's going on there, or should it work and I've just messed something up?

Thanks!