Hi @wissal ,
IMHO, NVR is Network Video Recorder. and Huawei VCN have all NVR Function with more advanced features and functions, so can be said that VCN is an Advanced NVR from Huawei.
For your scenario that some NVR also installed when there a VCN, there should be some different policy or different usage of NVR and VCN.
example; there are 256 camera connected to VCN, we can install a 32channel NVR in a department and directly get video access from camera only to view 32 Camera specificly and we dont need to make some changes to VCN or give VCN access.
And many more example.