1995 appears to be the first hs featuring the 61 for TsNIITOChMASh. The prior ones were 539 (TCW).
Most likely 61 is not making the cases themselfes and they are still made by others with the code 61.
The mid 1990 are the time when TsNIITOChMASh started using the own code rather than taking readily available cases like in Soviet days. Before that the 61 was only seen on tins and crates while hs inside were random Soviet.
Might be related to the then upcoming understanding of own branding and the commercial identity of companies.
Out of 1996 we know the hs “61 96 9x21”. Meas the “Г” (Latin “G” - likely for Gyurza) was dropped later (after 1995).
1998 headstamps are standard pattern “61 98” (have not seen 1997, sure may exist).
Our Russian friends may clarify.