Multi-stage sandcarving is more of an art form and one that requires dedication and practice. In general, multi-stage carving is done on cutting vinyl, and you progress one shape at a time, carving to the desired depth and shape.
The rule of sandcarving is you can only blast half as deep as the width of a line or shape before that shape turns into a V cut, so learning to use blasting media to shape the glass in realistic form takes dedication and a particular skill set.
Tackling complex projects using photoresist takes skill at the design stage. You don’t want etching lines that cross over each other. In general, multi-stage sandcarved images are simple line art patterns without many open areas.
A good rule is blasting the same item several times until you develop what looks most desirable before producing the final piece, all while working backward because you can only truly appreciate multistage carve items looking through the glass surface.