This is actually something Donruss/Leaf was doing back in the 1990s - they would create a set, number it to, say, 1000. Then take the first 250, and die-cut them, and call them 2 sets. So the die-cuts would all be 0001/1000 - 0250/1000 - only 250 in the set (PR250) yet serial numbered to 1000 (SN1000).
We consulted with Admin when it came to formatting those sets, and using the PR/SN combo was deemed the best way.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).