Ok! So in catching up on all but one (The one with the aviatrix coming forward in time) episode of Torchwood, this here seems to be Jack's general timeline. The blocky little railroad track bits are him taking (to quote Mme. duPompadour) the slow road.
A= Someone is born on 51st Century Earth, grows up, is recruited into the Time Agency. At one point he decides that it's far more fun to have fun, so
B= He toodles around in time as a free-agent for a while, until he...
C= Goes back in time to 1941 to cash in on a crashed spaceship. Here, he takes the name of a recently deceased RAF officer and is hereafter called "Captain Jack Harkness" (even though that's not really his name). Things don't work out quite like he planned since he..
D= Gets picked up by Doctor Who for a few grand adventures.
E= He goes up to present-day Cardiff to save the world, finds out about the Rift in Cardiff, then gets whisked ahead to..
F= The far flung future. Here, he's made immortal by Rose (with a little help from the Eye of Harmony, and thus from Rassilon), and is abandoned by the Doctor so he can help rebuild humanity in the.. year 200,100 or so. That'd be the 2,000th Century, wouldn't it? After things seem well in hand there after some years (he's immortal, so it may've been a hundred years, may've been a thousand years), he tries to head back to a time he's more suited to (like the 51st Century? Or the 21st Century?) and instead ends up in..
G= 1869. His little time-hopper jaunting unit isn't quite so happy at the moment, so he's stuck there. But for better or for worse he's now immortal, so...
H= He hangs out for a century and a half (yes, he passes himself since this is his second time through 1941), hooks up with Torchwood, where..
I= He gets sucked back to 1941 for an evening (this doesn't overlap with his first time through, since he meets the not-yet-dead Jack Harkness. Still, it's overlapping with when he "recently" had to take the slow road). End of Torchwood's first season, he hooks up with the Doctor again and...
J= Goes to the year 100,000,000,000,000 (give or take) for a bit.
K= They (of course) save the day and Jack is returned to the present-day timeline.
I was a bit confused about the name-adopting bit, but then I realized that just because he said (in the 'I' instance above) that he took the real Cpt.Harkness's name when in 1940s London, that doesn't mean he took it the last time he was in 1940s London (when he was taking the slow road). Tosh probably (and understandably) thought that Jack meant he was using the fake name for 60-odd years, when actually he's been using it for far longer than that -- at least 160 years (all the years taking the slow road from 1869, plus all the years spent in 200,100).