ZR is a wrong transcription and should not be used.
We had this issue in the old forum already.
The official designation today is “PZ”. The latest hs I know of is “17 75” and so far I have no Russian source mentioning it’s recent production and also no catalog where it is described/offered.
The history of the cartridge and it’s designation goes back to the early 1930’s when the “incendiary” and the “spotter” were still two different cartridges with different designations and markings. Technically the cartridges were identical in it’s internal construction, just the chemical fillers were different.
Here the designations and markings over the years:
From the beginning in the early 1930’s:
P = Spotter (WP), white tip
Z = Incendiary, red tip
From 1935 on:
Both projectile effects were combined to an incendiary-spotter round and were designated:
ZP = Army designation (red tip)
PZ = Air Force designation (red tip)
In 1941 the designation was unified to “PZ” and is still in use today.
It would be interesting to hear if somebody has a date later than 1975.