Did you guys notice any wing feather molt on your late 80's Clark's Grebe? If your bird stayed that late into the winter, it may have been "staging" earlier that fall, like I believe the Smithville grebes are doing now. I bet the current Smithville grebes hang around for a possible CBC record.
The current Smithville grebes won't be gone tomorrow, because they (at least one of them, anyway) can't fly.
Regarding the appearance of the Iowa Sabine's gull from last month, I don't see why a full hood on an adult would be unusual at that time of year. Based on the information I have available to me (Dunn and Howell, mainly), adult Sabine's gulls retain alternate (breeding) plumage until they reach their wintering grounds (off the coast of Peru and Chile). They then molt into basic (nonbreeding) plumage while on said wintering grounds. There is a partial prealternate molt early the next spring (while on winter grounds) that essentially produces the stunning alternate plumage. I found a paragraph that mentions the prebasic molt does start with the head feathers and may start earlier on some birds (during fall migration), but this is variable.