In some very rare cases, there is documentation from MS, as you saw. The Exchange Server SDK gives you at least some symbolic names, Outlook Spy knows a little more by name OpenMAPI has some names, some float on the network.
As far as I know, there is no final complete list.
Editing:
If you were looking for mapi properties from OOM, Outlook Outlook should name most of them. It has a 30-day trial period and quickly becomes invaluable when working with Outlook.
And no, I do not get the position;)
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