As far as I'm aware, full-suspension Oranges were, and are, built in the Orange factory, so their serial number format is completely different to Taiwan-built frames. As the 2000 range went on sale late in 1999, you would expect most of the 2000 frames to have 99 serial numbers. I would guess they build them at a steady pace during the year, and accumulate stock until they've got enough for the release of the new model year each autumn. If so, you might expect 2000 frames to have been built during most of 1999.