Yes, I think that once this caper started then 00 was domestic. With the older paper serial number labels it doesn't apply, even if the model number is five digits, such as Addams, 20017. There's simply an upper-case 'I' in front of the individual number for export production, without specifying where. The label on the shipping carton did have the destination on, in red ink.
I looked at that listing, and found that Earthshakers with serials close to my old one are noted in Australia and New Zealand.
One thing I noticed on that platform was that in places the destination identifier was mentioned as being subject to debate. It seems clear-cut to me, having unpacked a few games, both u.k. allocation and not. The games using WPC-S even have a page at the front of the manual, explaining the presence of the security chip and picturing the i.d. display when starting up; "the model number is shown without the country specific code"