I have encountered this problem before, and I finally solved it like this: 1, when inserting endnotes, you don't use customization, but automatically insert them, so that the serial numbers of documents will be sorted in turn, especially when you add another document between 1 and 2, the serial numbers of subsequent documents will be added in turn, which will not affect the typesetting; 2. Where you want to add multiple documents, add all documents according to the method in the first step, as shown in figure 1, and then leave only two serial numbers. Select the middle serial number and right-click the font to hide it, so that the middle serial number will be hidden, not displayed, but will not be deleted. It still exists in the endnote section, and then it is marked with "-"in the hidden section.