I think I just may have had a moment of enlightment: Full Body Morphs (FBMs) are not really morphs but control dials that affect the figure "globally" or "remotely". The "real" morphs are in each specific body part that they were created for, i.e. partial body morphs (PBMs). As the head is a specific body part, combined morphs from M2 may be transferred successfully to M1 without the original M2 morphs being present in the target M2 CR2, i.e. the combined morph consists of the relevant M2 morphs being copied over. Doh!