Short answer: v1.9 was a beta version of DS coded for the upcoming BG2 Fixpack. It was available publicly for about a month before being pulled (more below).
Long answer: v1.2.4 was the last of the 'old school' releases that overwrote the files. The spells were based off the Baldurdashed ones, AFAIK, but they did overwrite spell files which made them suboptimal for modern use.
Flash forward a bit. The BG2 Fixpack is commenced, and we decide to incorporate several under-the-hood changes for modders as a separate component in order to fight the fragmentation of common tools such as DS. In keeping with the Fixpack approach of overwriting nothing, DS recoding (completely patching instead of overwriting) is completed in March, based off v1.2.4 from cirerrek's site. The Fixpack is still not publicly available, but this DS is used by a few of the modders on the Fixpack team for various mods (Kish's Oversight, Sim's QP). This is released publicly in September as a standalone package, dubbed DS beta 1.8, and goes through a few point releases to v1.91.
In the meantime, King Diamond has been working on the same issue, using the slightly more evolved version of DS used for the Big Picture family of mods. It's released standalone as BP-Detectable Stats v1.1. The Fixpack version is withdrawn over larger community concerns over Yet Another DS Fragmentation.
Between the two, momentum builds for expanding detection beyond spells to items and other goodies. A newer version, temporarily dubbed "Detectable Affects" [sic], is under development at G3 in our
development wiki, combining the strengths of the two modern versions and expanding the capabilities of detection. The version under development, once completed, will be the one included in the Fixpack.