I’m not familiar with most KV-1/2 prototypes (U-0 - U-19) due to a lack of sources. Important to note is obviously that these prototypes were continually changed and their turrets got switched around a lot. But for example the KV U-7 had a cast turret and L-11 gun at some point. KV U-11 and U-15 had a cast turret with F-32 gun. The other prototypes may have had interesting features too.
Two KV-1’s served as prototypes for the V-2KF engine with 650hp.
There’s the ZiS-22 armed KV-1, with prototype ZiS-5 gun using F-22 barrel rather than F-34 barrel (long story). And another KV-1 (mod 1941?) was tested with an actual F-34 gun.
There was the electric transmission KV tested in 1943-1944, dubbed EKV. Mostly as a testbed IIRC.
KV-150 and KV-220 were both called KV-3 at some points (KV-220 was even called KV-4) and I think better fits under the KV-3 umbrella.
The IS-1 prototype that was referred to as the IS-3 was not the third prototype. I’ve only seen it been used to describe the first prototype, but this is merely a coincidence. The name referred to all vehicles of this type. This was because the object 233 at the time was known as the IS-1 and object 234 as IS-2. Hence why the object 237 was IS-3. Hell the IS-2 was also at one point in development called the IS-3.
There’s the IS-2 prototype with T-shaped muzzle brake, and the early production IS-2’s with Ferdinand type muzzle brakes. All these were armed with the early version of the D-25T that still featured the screw breech design.
You have forgotten the original object 703 prototype, most commonly known as the Kirovets-1. The IS-3 without the pike nose.
The third IS-4 prototype (object 701-3) was just a chassis and turret, without gun or engine, used for firing trials. It had a different armour layout compared to the first two prototypes (and also later). The trials from the first two prototypes served as a basis for the fourth, which received improved transmission. Then that prototype led to the fifth that received the new turret and improved hull armour, and finally that was refined into the sixth, of which I don’t know the major differences. But this info also suffers from bad sources on the subject.
The original T-10 was the IS-5, not IS-8. And IS-9 and IS-10 were never names for the object 730. IS-8 was the last before Stalin passed away and the destalinisation began. There were also command versions of the T-10B (T-10BK) and T-10M (T-10MK) with radios replacing some of their ammo stowage.
Object 265 was another T-10 prototype, though extremely unclear what it was due to poor sources, it was either a testbed for the M-62T cannon, or a highly modified D-25T called D-25TEh. There’s like three dozen other T-10 prototypes that tested different transmissions (709), nuclear protection (756), floatation devices (755), fire suppression system (739) etc. etc. Though not as interesting for WT.
Non-named prototypes also exist, a T-10B was supposedly improved with the V-12-6B engine (750hp) of the later T-10M, and another T-10 prototype (object 267) was supposedly improved with a modified V-12-6F engine delivering 800hp.
These were the things that were built, but you seem to include paper designs too.
There were of course several other projects to fit different guns in the KV, including the 76mm F-27 and 85mm ZiS-25 that never got built. Not to mention how the 122mm OBM-51 (later renamed BL-13) was originally planned for the KV chassis.
When the IS-1 was being developed there was a counter proposal against it, that essentially redesigned the KV-85 to have a single plate sloped UFP. Can’t remember if it ever made it to paper.
I would add the object 752 and object 777, never built, but designed as successors to the T-10. Both had atleast two designs IIRC. There’s also the 100 tonne version of the 705 that supposedly received the object 718 index.
The hyper velocity 85mm Strela project also encompassed object 277, 278 and 770. And the 770 was also supposedly part of a project for a 140mm smoothbore version of the M-65.
