The East German AF used local designations if confusion could arise.
For example, when the East German AF MiG-21PF was modernized with the RP-21M radar, the new designation MiG-21PFM was used by the East Germans.
When new MiG-21PFM aircraft were delivered to the East German AF, this MiG-21 type was designated MiG-21SPS (and SPS-K).
So local designations were used by the East German AF.
Jeroen