Session count limitation for NVENC on Quadro K1200

The NVENC cannot support more than two sessions on low-end GPU, is K1200 low-end ?? I can open 13 simultaneously sessions on Win7 .however on CentOS7 ,it cannot support more than two sessions, the SDK is NVENC SDK 6.0 and CUDA

Toolkit 7.5 . can anyone tell me why ? forgive my poor english ,Thank you.