Thanks for the hints. I've completed the Fort House and it takes me to Dino Valley alright. The thing is, it takes me to Dino Valley 2, not 1. From DV2 (which is a yellow level) I get to the Valley House. A new yellow dot did appear over DV2 but there's no way to get to it. There's also a dark green spot for a new level above DV2 but I can't get there either. I have gotten the exits from DV2, Valley House and Valley Fortress (two exits in the fort).
Screenshot.
EDIT: There is no lava in Frosty Cave 5, maybe you mistook that for another level?
EDIT2: No, wait, yes there is. I'm a moron, sorry.
EDIT3: Found them both, thanks. FC5 was just evil, but I can't believe I missed the pipes in WF3. I think I've found all exits now, although it's hard to tell because the starting screen still shows only *96, which is a real shame. Still a brilliant hack!