Yes - that is effectively what I am asking - to calculate the RA/Dec offset in the miss - and compensate for it in the next slew. This offset is only needed during the centering process and can be thrown away once it is done. Using sync/slew to do this has no particular advantage - and it has many disadvantages.
There is no need or real benefit to doing a "differential" move. Mounts need to do a full slew to correct for backlash - and that is to a specific RA/Dec location. SGP just needs to subtract the measured overshoot in the RA/Dec values and slew again - instead of doing a sync and repeated slews to the same target RA/Dec values.
Frank