The GUID probably could have been shorter, that is true. However, even searches on substrings within the GUID should yield unique results. For example, the first n characters of the string.

Nova

Nova, I'm afraid not. Google searches full words only; it's not (as one might think) like searching say within a Microsoft Word document which finds substrings. In other words if you search for "abcde" you will never find "abcdefghij" (unless of course both words happen to be on the result page). That's how Google works at the moment and there's also no way to use a wildcard character within a string (though you can use one within a phrase, "like so *").

Turns out that Google *is* indexing the full GUID

So I've reinstated it

N

Yes, Google will index the full string (or parts of it). It just won't index sub-parts...