Bacon Bits
Legend
So, I understand why they did that in the past. In the age of analog, if you have multiple listings for a thing (say "circular logic," and "logic, circular"), then if the base text changes, you'd have to update manually both listings in the index with new page numbers, and any manual process like that is prone to error. If you have the index refer to itself, when page numbers change, you only have to update the root references.
Today, there's no frelling reason for this. The referencing can be to an anchor, and the layout software can render to whatever the page ultimately winds up being.
It's also like they didn't quite understand the point of cross indexing, though, too. Like an encyclopedia listing for gunnery says see also ballistics. Ballistics says see also range finding. Range finding says see also surveying. Surveying says see also photography. So now there's a link between gunnery and photography. But each entry also lists a page number for that topic's article. So armor proficiency might say see also feats because there are feats that grant armor proficiency. Spell lists might say see also classes because classes have custom spell list modifiers.
The real crime is that they haven't fixed it in subsequent printings!