NEC DS8000U VCR where to find manuals? Belts? Codes?

[Electronic M]

You're making some right and wrong assumptions...
Top loader era VCRS used a mechanical counter tied to the drum reel which advanced a certain number based on take up or feed reel rotation. The normal count is designed to mimick that. Later decks usually used the linear control track to perform Real Time Count and to perform tape counter indexing. VHS tape is typically divided into 3 sections...2 thin stripes along an edge for the linear audio and linear control track read by a fixed head like an audio cassette, and then there's a 3rd region that comprises most of the width of the tape which contains a series of diagonal stripes of video information from the spinning head drum.
If it's reading only the control track then unrecorded sections of tape won't advance the counter even while playing.
Better mechanisms have 3 states to threading: 1.) completely in the cassette, 2.) Capstan and linear head only (Stop-fastwind mode), and 3.) Video drum, capstan and linear heads (playback and visual search). If your mechanism doesn't have state 2 and reads counter off the control track then it has to keep everything threaded to maintain tape count.

The control track was initially a IIRC square wave tone signal designed to aid the head drum and capstan servo in duplicating the tape speed and phase and the head drum speed and phase such that the video head would be able to correctly trace the recorded video stripe (instead of say tracing between 2 stripes and getting noise) when LP and EP/SLP came out the frequency of the tone could be used to figure out which speed, and as digital electronics got affordable engineers started using those digital electronics to count those pulses which were directly tied to frame rate and there's 60 frames a second...So accurate time could be kept (as long as there wasn't long unrecorded static between recorded portions). Eventually they even added indexing to the control track and made provisions to dub index marks in and out.