Yes, that explains it a bit better and changes the issue.
Yes, the fix is very simple; but I don't see a way to fix it other one at a time. However, you should be able to do it with a minimum of key strokes by doing the following:
1) Create the source in the Source Workspace
2) Now select the "unlinked" name near the bottom of the list of sources where the unlinked items are.
3) Now, select the first citation (in the middle panel) and right click > Edit. Then type the first half-dozen or so letters of the actual source you want to use until it pops up in the source list.
4) Select ok. That should attach that citation to the new source.
Go back to the Unlinked source and repeat 3 and 4. You will get pretty fast at this after you've done a half-dozen or so.