Ok - now you asking a question we can get our arms around.
From what you said, it seems you want inbound telephone number ( lets use 555-666-1212) to ring in on many desks. If I got this right, then the answer would be that the inbound number (555-666-1212) would be Inbound Routed to a ring group that has in it all the extensions you want to ring for this number.
Well that is traditional way to handle it when you have a Private line - an individual who has a phone number that rings directly at their phone without any IVR, or ring groups.
As has been said by Boolah, Just enter the DID in the "Add Inbound DID" field on the Extension's page. The inbound route will automatically be created for you.
So - for number you want ringing on multiple desks - The inbound route destination for the number is a ring group. For private line use, the inbound route goes directly to a single extension destination.
Unless - I'm failing to understand your situation again.
So, step by step, here's what happens (and which way to get it to work):
If I just go in and created an inbound route for 555-666-1212, I get an error saying that "A directdid for this DID is already associated with extension: 1212 (Ken Linger)." I then cancel the creation of the inbound route and go into my extensions, select 1212, and can see that for the Direct DID field, 555-666-1212 is listed (this is how that extension gets calls without going through an inbound route definition).
So, if I blank out the Direct DID field on extensions, save my extension, go back to inbound routes, I can create an inbound route for 555-666-1212 and point it to my extension (and of course, select Superfecta as my CID source because that's what this entire string is about!).
Assuming that this works, then I should go ahead and do the same for the other 99 extensions? If it works, great. (Pain to redo 100 extensions but fairly simply moving forward)