did they approach you, or did you have an agent shopping your stuff around, or was it some other thing that got you in their sights?
My agent pitched me to them (he is absolutely amazing). Interestingly, a reviewer had passed the first book to a (different) editor at Tor two years ago, but I never heard anything and I doubt it got read -- I just shrugged and moved on at the time. Working with my agent has been an incredible experience; he handpicked the editor who would match well with the series and really sold me to her.
I'd actually be interested in hearing (if you're willing to share it) one step back from that and if you decided to query agents or if you got your agent through another path.
I got unsolicited but serious major movie interest in the series, actually. I spent about a day freaking out and wishing I could get someone else to handle the communication for me, and then realized that those people exist and are called agents and I should get one! I emergency queried (mostly through referrals -- community is SO important!) and had three offers within the week.
(For example, I know Hugh Howey's agent approached him after reading his book.)
Prior to this, I actually have been approached by two different agents after they read my work -- one from a short story and the other from Zero Sum Game. But both wanted a new novel to sign with rather than something that was already out, so I was keeping in touch with them and working on other projects to pitch to them at the same time I was SPing this series.
And if you did query, did you do it for this series or a new one?
It was for this series, because of the movie interest, but my original plan had been to finish something new and query that in order to hybridize myself. This just happened before I could do that...
Most agents I've heard in recent years have said they'd be fine with repping someone who had self-pubbed but that they normally aren't interested in the already self-published series.
This is exactly my experience. I've actually had not only interest in my writing from two different agents before this, but two different fairly major publishers (not Big Five but one step below that, major independent presses with big name authors). But they also wanted something new, not a previously-published series. I definitely, definitely, DEFINITELY do not recommend self-publishing as a route to a trade deal on the same book. (More on this shortly.)
But I did recently hear a Tor editor say they'd consider an already self-pubbed series depending on the numbers so it seems to be a constantly shifting target.
What mattered more in my case is how much my editor loves the books.
My numbers are not actually big enough to be like, we should pick up this author just based on that -- my sales are in the 10^4 range (tens of thousands, I mean) but my understanding is that they're still not at the sort of number that usually gets picked up. I think in my case, they see there's a lot of potential (and enough sales to be serious) and an audience that hasn't yet been reached/saturated yet. But no, I'm not at the numbers people usually cite for "this is how many books you need to sell to interest a publisher."
More to come -- I'm trying to write up a more informative post about how this all happened without publicly giving details of anything I shouldn't be.