I honestly think that's pretty rare when a steady dose is maintained. I've met a lot of FTM's in person recently getting involved with activism, and the subject came up. Of the guys who'd been on T for a year or more, no one had gotten anything more than a random spot or two, and the spotting was only one guy in his first year when they were adjusting his dose and injection frequency due to acne. One guy had been a female bodybuilder pre-transition, and he said even a quarter of the standard dose is what he and other off-season bodybuilders needed to keep menses away long term.
From what I've seen mentioned on this forum over the past year or two of lurking, menses returning seems to be more common in those who had reproductive system issues pre-T like PCOS and Endometriosis. I had ('have' I should say, I'm certain T didn't cure anything) both so I'm always nervous that it's going to come back at a really inconvenient time (as an aside; since I pass 100% of the time now, that would be anytime). I'm already looking into FTM friendly gyno's to help me get this junk out covered by insurance though since it's all jacked up and diseased anyways.