As I understand it, what happened was that the 690A was clearly a home run-- and I think the top-selling turboprop for a few years in the 1970s. Once they had that, they went out and surveyed the customer base about what they did and did not like.
Then, like any smart company, they put together a product road map. The first step was to redesign the wing to eliminate the fuel bladders, and also the corrosion problems which were starting to rear their heads. They also went with a new technology, light weight air cycle machine, which both reduced the empty weight (as did the wet wing), and increased greatly the baggage space. A customer complaint was useful load with full fuel, so they improved that. Step one.
Step two was adding the -10 engines, which gave a big boost in performance. These airplanes became the 840 and 980.
The next big thing that Commander customers complained about was the pressurization, especially since the -10 engines gave them the performance to operate in the 30s. So step 3 in the product road map, now that they had redesigned the wing, was to redesign the fuselage so that it could accommodate higher pressurization differentials, and while they were at it, increased the cabin height and lowered the noise levels. They were also able to take back some of that large baggage space and make an enclosed bathroom, another customer request.
The combination of the redesigned wing and the redesigned fuselage was the 1000. In the recession of the early 1980s, there was demand for a cheaper version of the 1000, which was easily created by putting -5s on the 1000 airframe and creating the 900.
The last step in the product roadmap was an airplane which could cruise faster in the mid-30s, ideally around 320-330 knots, to at least keep up with the latest competition, the Cheyenne 400LS. This airplane would also have higher weights, to give it better range with more passengers, and a higher landing weight.
This was going to be the 1200, but the -12 engines it relied on were never able to deliver the power necessary, and it's not clear that even with the power they would have delivered the speed to keep up with the 400LS. However, Commander was able to complete the engineering on the weight increases, and this resulted in the 695B (or 1000B as it is sometimes called). This was the ultimate Commander, and according to a presentation I saw, checked all the boxes of the 1200 except for cruise speed.
