It's not a projection of how many submarines are desired or funded. Nor how long it takes to assemble a submarine.
Given what is known about the size of the facilities and their layout, it's speculation on the maximum number of slots that could be used, whilst also maximising efficiency (whether new construction or maintenance) in terms of cost/time. In the Chinese commercial shipbuilding industry (and indeed in other Chinese industries), they're obsessed with efficiency and driving down costs.
Always leaving a spare lane next to the side of each submarine means that:
1. large components or modules are always able to move to a submarine
2. an entire assembled submarine can always be moved to any other location for the next stage of production. (At a minimum, we know there is a separate building for painting and anechoic tiling)
So this means any permutation of production flow could be applied
Okay, let me put it more starkly -- the point is to actively avoid trying to come up with "optimistic" projections of forthcoming PRC nuclear submarine production simply because some of the permutations of production can viably offer a higher production rate.
The cardinal sin of PLA watching is setting expectations too high and then having to walk them back.
I think we can go a step further with:
"Given an established nuclear attack submarine design, Bohai Shipyard has recently demonstrated the capability to launch in excess of 3 submarines annually"
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It would also be factually accurate to add:
"Furthermore, we can see that Bohai shipyard has undergone a significant expansion with new submarine construction facilities.
This expansion includes completely new submarine assembly buildings which cover almost twice the land area of all equivalent buildings in the US combined."
I would say "may be able to launch approximately 3 submarines annually" to account for lack of longitudinal imagery which means we have to account for the possibility that some launches may be prior boats returning to drydock->pontoon->hall for maintenance work.
I would also say "actual procurement rate" will depend on funded boats, ability for a sufficiently sized personnel pool to keep up, and dependent on technological maturity (especially for new designs like 09V, 09VI).
All of which is another way of saying for everyone to be cautious about what the projections for actual near term PRC nuclear production may be (even if it is going to be much higher than say, between 2006-2020).
