Even char_id, account_id, & npc_id is overlapped, it doesn't matter, because they used for different matters.
Well besides minimum char_id value that we believe is as AEGIS style, however, don't ever make it less than 256, as we can see, in some case, item that impossible to have slots (forged, named, egg) NEEDS card[0] for CARD0_ src/map/itemdb.h#L28-L30
So, afaik, don't ever make the minimum ID less than 256, for now.
and btw, so we can judge that script has wrong behavior then, to check if the items is BG items (but it's not official issue here)