When testing a method to exhaustively search regiments, I decided to try it on this regiment, as well as other already known ones. It turn out that there are several interesting things about it.
First of all, the polychoron ipi is the blend of three srits (o3ox3o4x), blending two to a vertex figure. The octs blend out. In fact, this is what happens when gico, the compound of three tesseracts, gets cantellated and the 2octs get removed This is already known, but it turns out that 6 out of 7 srit regiment members can do the same thing. Rawvatoth blends to ridi, spript blends to sarnipadi, garpit becomes sirc when the ops blend to srohs, and pattinoth and pinpith also become nadupti and dupapdi respectively.
The remaining member of the srit regiment is sirdo, which is interesting because instead of forming a blend it forms a compound, which also has coinciding edges I just looked up this compound of 3 sirdoes and it appears to be called sepdi, for small prismatodisicositetrachoron.
There is another way to construct sirc. Since garpit is a blend of three odips (octagonal duoprisms), sirc is a blend of nine odips, blending 4 to a vertex figure. I wonder if there is a similar compound of nine square-octagonal duoprisms or even tesseracts.
There is also a way to take a compound of ridi and ipi without faces or cells coinciding. As this is very clearly an "inter-regimental" compound, I would like to know if there is any important reason why it was not mentioned here while a similar compound in the o3o3o3x3o3o regiment was. In fact, this kind of compound seems to be pretty common. I've seen a few of them when I searched the gacoca regiment.
Finally, half the cells of sirc can be removed and all the original faces will still be in place, each incident to one cell instead of two. This may be known as well, but I thought it was interesting how it shared this property with hex, dittady, chon, etc. Unfortunately this leads to no other company members.