Well, I can see why he'd have wanted to join Torchwood before, because Ten appears earlier (face-eating televisions, anyone?) But it just doesn't look like he did. I'm leaning towards Jack having been a prisoner of Torchwood's before Canary Wharf. Partly because it would have been really cool if Jack was pulled out of the wreckage of Canary Wharf along with Ianto and Lisa. But mostly because it just seems to make sense.