So I managed to find a serial number inside the powerbook on the motherboard. There is a larger S/N sticker which probably corresponds to the board itself (there are other stickers like that one on the various components). But the smaller print one resembles the general format of Mac serial numbers, although it does seem to have an extra digit. Any chance anyone knows how to decode it? I know the first two characters mean manufactured in Cork, Ireland.
Here is the full s/n: CK50613T2U88 (or BB? see picture)