Wilford retired from Confederation service just after the Kilrathi War ended (in 2669). His last post was as a line Captain (O-6), supervising command of the Enigma Sector. He moved to the Border Worlds to spend his retirement. When the Border Worlds decided it needed to build up a fleet, their government offered him a comission as a Vice Admiral (O-9). When he returned to Confederation service to command the Midway, he returned to his last Confederation rank -- Captain (O-6). You can tell that WCP refers to the rank and not the position by looking at his rank insignia during the game (single silver bar).
The 'real' reason Wilford becomes a captain in WCP is because the role was written with Eisen in mind -- when Jason Bernard died, they switched it to being for another familiar (but certainly less celebrated) commander, Wilford.
Blair's reference to Tolwyn as a Space Marshall was purposefully sarcastic, though -- it's actually written in single quotes in the script, for emphasis of this (As in " 'Space Marshal' Tolwyn ").
Of course, were you to look at Tolwyn's service record circa 2673 (after his death), it would confirm that he was actually promoted to Space Marshal...