It is true that in the somewhat fifteen years of its existence as fully privately operated company, GO has released an astonishing number of beautiful and very well-made movements. However, not every reference in the catalogue has its own totally independently designed and manufactured movement. GO watches are based on a number of movement families, each with its unique merits and capabilities, and "individualized" by different complication modules.
The Senators were until now based on the cal. 39, which is a completely re-designed movement, originating as cal. 10-30. Here is an article narrating the development history of the cal. 39:
The cal. 39 was found in all Senators, including the chronographs, which had a chronograph module, as well as in the Sport Evolution watches. The various complication modules, such as power reserve, moon phase, and the perpetual, were all developed and produced in-house in Glash?tte, and also set atop the cal. 39. Only now, beginning with autumn, the new cal. 100 will replace the cal. 39, preliminarily only in the Senator series, while the Sports Evolution keeps the tried cal. 39. One reason for this decision might lie in the fact that the cal. 100 has no date quick-setting via the crown, but via a separate corrective pusher. This pusher, as well as the second one, responsible for the unique second-reset function, makes it difficult to use the movement in a sports watch with extensive rating of watertightness.
The development and presentation of the marvelous cal. 60 and the PanoRetroGraph marked a distinct step in the history of the company. While the Senator series focussed on the more conventional watch design with perfect everyday capabilities (automatic, reliable movements that was a good base for various complications), the new Pano-series presented a new approach to high-end watchmaking in the company. The PanoGraph's cal. 61 shares some basic layout elements with the cal. 60, yet necessitated massive reconstrution in most areas. The PanoReserve's cal. 65 is unique, as is the cal. 90 of the automatic Pano-watches. This is again a movement family in itself, offering the capability to add complications, such as the moon phase or the power reserve indicator.
All round-cased 1845 watches were based on the cal. 49. This movement is very well designed to be used in a various of ways (small second, centre second, regulator, to name but a few), as can be read in John's marvelous review of the Union Glash?tte Bergter, which uses the smae movement base (with different finish, though) as the 1845 watches:
Then, there are the shaped movements cal. 42 and 21, both handwinding movements. The latter is the small movement for Lady Karrees. It will depend on the popularity of small ladies watches, if the production of this movement will be continued, or if the larger men's watch movements will be used.
Finally, the specialities: You spoke about the tourbillons. You are correct in stating that it is hard to imagine how the company could develop and release tourbillons in such a short time, while at the same time developing other movements and complications. While it is possible for a good master watchmaker to produce a tourbillon as an individual piece, by just fiddling around so long, until all parts fit, a series production is far more difficult to realize. Therefore, it is common to entrust parts of the development of series tourbillons to the few experts in this field. UN has Christopher Claret, Lange had Renaud&Papi for its "Pour le M?rite", and GO had Paul Gerber, at least for one of its tourbillon models, while the new PanoMatic Tourbillon has been fully developed in-house (the manufacturing of all parts always was done in-house in Glash?tte!).
So you see that a rather large variation of complications is possible by making use of several movement families. However, already these base movement families are so numerous, that the effort to develop and produce them within such a short time deserves the highest respect.
Hope this helps,