EndNote assigns a unique record number to each reference as it is added to your library. These record numbers appear in the temporary citations to ensure that the correct reference is used when the paper is formatted:
{Argus, 1991 #31}
The record number for a reference is also visible in the title bar of the Reference window.
You may also see record numbers in the Library window by selecting Record Numbers as one of the display fields for the Library window. See Display Fields.
Because these record numbers are so important, keep the following points in mind:
We recommend that you do not rely on EndNote’s record numbers as a means of filing or numbering your office reprints, because you have no control over this number, and it is subject to change under certain conditions (read on). Instead, enter your own unique number into the Label field, or any Custom field, and use that number for your reprints.
EndNote automatically assigns a record number sequentially to each reference as it is added to a library.
If the same reference appears in two different libraries, the record numbers will most likely be different.
The record numbers are never reused or reassigned within a library. If you delete a reference, that number is never used again in that library.
You cannot modify or reassign record numbers.
If you delete a reference from your library after you have cited it in a paper, EndNote will not be able to find it when it tries to format that paper. If you add the reference to the library again, it will be assigned a new, different record number, so EndNote still will not be able to find it when formatting your paper. You will need to reinsert the citation into the paper using the new reference in your library.