One of uncertain things about MPEG transport stream is if VBV correctness is still required when T-STD conformance is verified.
In other words, shall MPEG video elementary streams de-multiplexed from transport streams conform to VBV model?
If you read the specification carefully, the answer should be "Yes". ISO/IEC 13818-1 says that an elementary stream with stream_type=0x02 must be MPEG video and it should conform to VBV model according to ISO/IEC 13818-2.
However, from the decoder’s point of view, the answer might be "No". Since T-STD defines from input to decoder’s output, it can decode the stream without even referring to VBV.
It’s not an academic question. We got transport streams which conform to T-STD but not VBV. The customer asks us to stitch them together and multiplex again into program stream. Clearly, we need correct VBV occupancy values for each stitching points. Due to VBV problem, however, we cannot get these occupancy information correctly.