UDIMs are mirrored along the Y axis in UV space to allow for more flexibility when modelling and texturing. Inner mouth is a separate object. Eyes contain only cornea geo for reference.

For proper workfow, extract the LODs into separate objects. Use L1 for rigging and transfer the weights from it to L2 and L3. Use L3 for sculpting and rendering, and blend that shape back to the lower ones when finished sculpting so they sync up shape wise.