Game Data Library shows Sakura Taisen 4 sales at 257k. As far as I can tell there's only one SKU for it as no reprint or budget rerelease is listed. What listing(s) for ST4 do you see selling 20k to add to 277k total?
DC | Sakura Taisen 4 [All Versions] | 207.462 | 277.983 | SEGA | 21/03/2002 |
Even at 257k for ST4 though SW (166k) plus 20% PSN (33k) is still closer to ST5 (145k) anyway.