There have been some dragon encounters in DF Felltower. Here are the known and rumored dragons of Felltower.
Dragon Cave entrance Dragon - slain, dismembered, and the bits sold.
Sleeping Dragon - there is a large dragon semi-sleeping below the northern part of Felltower. It may be responsible for the earthquakes.
Cold Fens Dragon - there is a dragon that has been seen flying over the Cold Fens. Its lair direction is roughly known, but distance, and specific vector is not.
Sleeping Dragon #2 - there is a "normal" sized dragon - similar to the Dragon Cave entrance Dragon, above - that is sleeping in a huge cavern below a pit in the "gate" or "apartment" level of Felltower.
Lost City of D'Abo Dragon - the PCs were told there is a dragon in the lake in the Lost City. They have also been told there is definitely not a dragon in the lake in the Lost City. Brief investigation was inconclusive.
So far, that's in for dragons known or rumored. There has been relatively little progress on dealing with these dragons - probably because of the difficulty in killing the first one back in session 46. I have some thoughts on that, which I will post tomorrow. Suffice it to say the stats in DFRPG's Monsters and GURPS Dragons are not quite as lethal as the ones I actually use.