Ok, so now that I know how (thanks for showing me—and I agree, a silly place for doing exports, but I never looked further than File anyway, didn't think of Open much less Import), I tried exporting my own appointments to CSV.

Now, I notice you said you "confirmed the use, or in this case the non-use of quotes". Does that mean that in the CSV that you're trying to import back into Outlook, the email addresses (in column 11) do not have quotes around them? I'm being so specific because when I export my own appointments to CSV, there are email addresses in column 11; besides the header row there are two records, and in both appointments the email values are in double quotes. In the first there are multiple comma-separated addresses and some of them are names only, eg Bob Bridges (so I presume Outlook feels free to look them up in my contacts book), but others are email addresses; and in the other appointment the only entry is ...with the quotes. (That's my work address.) I infer that the quotes are necessary at import time. But you say you confirmed the non-use of quotes, so I'm suspicious.