Walt, Pete, I agree: busted call = no valid contact. If some information is missing due to QRM, QRN, QSB, …, repeat it or have it repeated until it is confirmed to be correct, or cut your losses, say “sorry”, mark the QSO as incomplete and move on.
Busted calls, however, are not only a question of phonetics, but occur often enough in telegraphy as well. Some people just seem to stick to what they want to hear … There was this Italian a few years ago who thought I was a New Zealander, and I am still not sure whether I managed to convince him that I was not one ;-). Some others seem to insist they hear a D where there is an L, or shorten an H, not just to an S, but to an I, or simply keep changing the order of the letters in the suffix, and no matter how often I say “no” every time and repeat my callsign, they still get it wrong. Well, then it is not my problem any more.
Regarding summit references: While they are not required for a valid QSO, I believe it is still a good idea for operators of any portable stations to repeat their location at least every few QSOs. For instance, I have got some entries in my log of which I know that they were SOTA contacts, but because the operators did not tell their location, I cannot enter them in the database until I get their QSL cards - if I get them at all.