That is capacity, not an production forecast.
Plus I don't think it would make sense to make more than 1 SSBN per year.
How many more SSBNs could there be?
I see a maximum of 8. And with a maximum of a 12 month module assembly time, that's an 8 year production run, which I think is a bit short for an efficient production run.
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As noted earlier, the ORF estimate of capacity is way off. A 9-12 month module assembly time would increase the capacity estimate by 3-4x.
- One might not build as many boats per year as the yard has capacity to do so, but one does not expand the yard if its not building as many as it has capacity to, and new bays are being added.
- It makes as much sense to build more than 1 SSBN per year as it makes sense to build 20 bays at Huludao, and there are 20 bays as Huludao
- There could be as many more SSBN as China deems necessary, which could be more than 1, or it could be it's 5x SSN + 1 SSBN a year, nobody knows what's in the bays.
- US builds 1.5 Virginia per year per 5 bays, multiply by 4 and you get exactly 6, so evidently your estimate of bay to boats per year needs rectifying.