Whether or not Jim Mundy was related to Doc Holliday, Toobworld Central thinks he was definitely related to two others who bore the Mundy surname: Alexander and his father, Alistair. And like Jim Mundy, both of them operated on the wrong side of the law for many years, as seen on 'It Takes A Thief'.
We may not have seen Jim Mundy's family in the 'Maverick' episode "Seed Of Deception", but that doesn't mean they weren't back on the ranch, twenty miles south of Bonita. He may have been divorced or a widower, but even if he did still have a wife, that wasn't going to keep him from carrying on an affair with the dancer June Collins.
As Mushrat would say, it's pozz'ble, just pozz'ble, that when Jim Mundy got out of jail about twenty or so years later (for trying to rob a bank), perhaps he became involved with a young woman who had corresponded with him while he was in prison, one who was enamored of his bad ol' boy ways. And perhaps, in a recognized union or not, she bore him a child in 1899.
Or.... If he had been married previously and had sons, then the theory of relateeveety would be that one of Jim's sons fathered a son in 1899 and named him Alistair. (His mother may have been prim and proper and the one intent on giving their son such a high-falutin' name. In fact, that son of Jim Mundy may not have inherited his dad's ranch and instead he may have gone back East, where the name of Alistair may have found a better reception for a young boy.)
Thirty-one years later, Alistair's own wife would bring Alexander into the world.
Unlike Jim Mundy, the two Als were given a second chance by the government in their career options.....