so, speaking as someone whose used these systems for decades, DVR files don't work that way.
The old, old school multiplexing VCRs did, sure. Those were recording to VHS's, and basically everyone swapped over by the early 2k's. What's hilarious is the reason. VHS tapes are expensive and wear out inside a few months- they've usually only got about six hours of recording, after which the rewind and overwrite. The high-end tapes purpose built for that might last four or five. back then, depending on how much data you had going, DVRs basically paid for themselves inside of a couple years (and the disks were expected to last a decade or so.)
In any case, modern DVRs have no gaps. They continuously record in a rolling loop- typically 7, 15, 30, or 90 days. The DVR is actually a server running on a network, and the server manages the data stream coming in, and maybe streaming to a client wherever the security office or whatever is. (or clients, even. It's all just software on the user end.)
there might be a system with digital storage tapes, and not hard disks, but that's really just a question of what digital media the data is stored on, and was relatively short lived. the digital tapes were used for very-large numbers of cameras.
For the record, the fact that we have a single camera that was released and not an array of cameras (or video cropped out looking like a blown up thumbnail,) is because it was a modern system.