In case you are wondering how tabs can end up after your endnote numbers, it can be easily done with a small modification to how endnotes are entered. This will give you the consistency you want. You want to replace the tab character (which apparently follows each of your endnote numbers) with two non-breaking spaces. If you want to have a consistent amount of space after each of your endnote numbers, the easiest way is to simply put the insertion point within the endnotes and then use Find and Replace. You will still have large spaces after endnote numbers that have fewer digits, but your longer numbers also won't run into your text as easily. If there is, indeed, a tab character after the endnote number, then the easiest way to fix this problem is to modify the default style used for endnotes (the Endnote Text style) so that there is a tab stop set where you want your endnote text to begin. This is odd, as the default behavior of Word is to follow an endnote number with a single space. The behavior that Patrick describes sounds like his endnote numbers are followed by tabs and not by spaces. But at endnote 1000, since Patrick's endnote text is justified, the space between the number and text suddenly becomes larger than it is for single-digit endnotes.
Single space each entry double space between entries. Put the word Notes (not Endnotes) at the top of the page with your endnotes. Be sure to use Arabic numerals (1, 2, 3) nor Roman (i, ii, iii). As the endnote number gets larger, it takes up progressively more space, such that at endnote 900 there is almost no space between the number and the text. The note number goes after all other punctuation. Patrick wonders how he can format endnotes to have equal spaces between the endnote number and the endnote text when he has up to 1000 consecutively numbered endnotes. Proper citation of sources is necessary to give credit to the authors whose work informed yours, to point readers to the sources you used, and to show the breadth of your research.