Perhaps somebody will correct me, but Robert April states he'd been a Captain for a decade sometime around 2239. That doesn't necessarily mean he'd been the Enterprise skipper throughout that time.
You're not wrong. From the scans I've seen posted, he only says he was a captain for ten years, not the Enterprise
's captain for ten years. Star Trek
conditions us to expect a captain to command the same ship indefinitely, but in real life, naval captains typically command many different ships over the course of a career, with command tours that can be as short as a few months.
Even in Trek, Kirk Prime, Picard, and Janeway are all known to have commanded other ships before the ones we knew, though in Kirk's case that's only from behind-the-scenes material. (The Making of Star Trek
said he commanded a destroyer-equivalent ship before the Enterprise
, and it's possible he only held commander's rank at the time, though he would still have held the title/job description of captain.)