The serial number for a Spoiler would 2 digits - the year it was finished - then an S, then the serial number. Even if you're misreading the 3rd figure, that would make it Alembic 465420, and I don't think they're to 15000 yet. Check the edge of the peghead or, more likely, the fingerboard after the last fret; I would expect the SN to be there.
Peter