For uploading photos, check the "website info" section of the forum frist - there are a number of posts there on the issue. See whether that any of them are helpful.
I do think there must be a mistake. The typo could be his (or the factory's). When I see two photos, I'll know what to believe.
In the early days, O'Day built a hull a day. Between '58 and '63 they had reached #1500. Probably used one mold, laminated, let it sit overnight, popped it out the next morning, laminated the next one. Just speculating.
Now, if that's the production method, then to do 1200 boats a year you need four moulds...
Look at the unofficial hull number list, in later years, the sail #'s do go up by about that much per year in the early '70s. The whole decade, from '69 to '79 accounts for 7000 boats (assuming no gaps in sail numbers). That's an average of 700, so a peak of 900 or even 1200 per year is not unimaginable.
When hull and sail numbers were handed out in the traditional method, they were not strictly related (as I learned from earlier, much earlier, posts in this forum). And the theory advanced, that people on the factory floor would just grab the next bag of sails and recorded the actual number on the plaque has the sound of plausibility.
If the DSII was built in a different plant, that would explain why hull number counting started over. But O'Day was also bought out at some point (owned by Bangor Punta for a while) so I'm not sure that the reason for the reset isn't one of change of legal entity.
One thing that seems to have been the case is that sometimes ranges of sail numbers were per-assigned to a model line or builder - to make sure, I presume, of no accidental dual assignment.
Therefore, my understanding is that it's not possible to use either sail (=class) number or hull number to establish a precise age relation across model lines.