is it possible for a heater core to leak but the carpet is bone dry.
Yes. If the heater case is well-designed and well built and sealed, in the event of a heater core leak the coolant will leak out of the drain tube, the same one that drains the condensation water from the A/C system in the summer.
I imagine you would still have coolant smell inside the car and steam on the windshield if it were bad enough.
Depends on where it’s leaking, too. If it’s at the seam of the ingoing or exit pipe and the configuration creates and easy path for the coolant to migrate out in front of the core, it could easily not wet the carpet.
I’ll get right to the point . . .
What are you symptoms?
May I assume you’re either losing coolant, and/or you’ve got no heat?
And if you’re losing coolant, may I assume you can’t see where it’s gone?
In other words, no visible leaks?
Yep. I drove my Buick down to Napa to check on a radiator. On the way home my heater core developed a leak to the point where by the time I got in the garage the whole inside of my car was like a sauna but no wet carpet. I like it when there is no question what the problem is.
If you do smell coolant (which can smell a bit like maple syrup if you’re not familiar with it), you want to get that fixed quickly. Breathing in coolant is best avoided.