I'm not really clear on the difference between headrights and patents, but this link seems to say that the headright was the precursor to the patent: https://wiki.rootsweb.com/wiki/index.php/Virginia_Land_Records Bringing new heads into the colony gave a person the right to land, and the patent (basically the title) was issued after the land had been surveyed and mapped. There were some other requirements too about planting the land and paying a "quitrent". Later on when labor was less scarce, it became possible to acquire patents by paying money instead of bringing people in.
If that's right, then John Bishop must have acquired his patent by bringing in these six people (not necessarily all at the same time), presumably to work the land for him although he could have sold some indentures to raise cash if he needed to. But his patent was abandoned (possibly because of his death), so the claim had to be renewed on his son's behalf. It's possible that any indentures that he held at the time of his death were also sold, if his son's guardian didn't have time to manage the farming of the land or didn't trust the workers to keep on working without a supervisor.
William Marriott says he paid 2650 pounds of tobacco and casks for Jarrell's indenture. I don't really know what that means in terms of monetary value, but it sounds like a lot. So Jarrell's indenture apparently had a lot of time left to run, while Marriott's indenture was apparently over.