I have been doing some tests to try to learn why Spotlight sometimes fails to find words in the contents of Microsoft Word .docx files. I’ve published some results from running a particular sequence of steps that on several Macs has exhibited the bad search results here: https://github.com/jafingerhut/osx-spotlight-test/blob/master/doc/README-test-sequence.md
Perhaps more importantly, I am hoping to convince people to vote on this issue on a Microsoft web site, in hopes that someone there will take a deeper look into the issue and fix it: https://word.uservoice.com/forums/304942-word-for-mac/suggestions/10998114-apple-s-spotlight-can-t-find-word-docx-files
Just click on the Vote button there. It only asked me for an email address in order to have my vote counted, and in the last week I do not believe I have gotten any new spam because of it (nor any email at all because of voting, that I can tell).