Only a few were domestic designs. Most of them were copied almost 1:1 from HP and Casio calculators, and adjusted for the inferior production capability. B3-38 in particular, MK-51 etc. Die shots almost match each other, and even the microcode was 99% copied with some fixes. [1] That likely was the reason they never updated the firmware.
The "Eggog" message was likely copied too, although I can't think of a good way to display an error in Cyrillic in 7 segments.
Home computers is another story, in particular the 1801 series which was a domestic PDP-11 compatible design underpinning most of the Soviet personal computing boom of the late 1980s. (it was slow though, holy hell)