Thanks to everyone for their kind replies. It has really helped me get through this long period of waiting to link my reservation!
I was finally able to sort of link my Swan reservation to MDE. Today tried again to do so from my Chrome browser on my PC and got the same "unable to find your reservation" message as usual. Then I happened to try from my iPhone and surprisingly Disney was able to find my reservation. Well, sort of! Neither my husband nor either of my children were listed on the reservation that was found. They were just listed as SD_GUEST_2, etc. In my original reservation made through Costco, their names are listed correctly. I was able to select them from my "Family and Friends" menu in MDE, but now I am afraid I won't be able to make Fastpass+ reservations for them when the 60 day window opens up. :-( Additionally, I get the message "Temporarily unable to retrieve additional details about this reservation" when I try to view it in MDE.
I guess it is back to the phones!