Finder and Spotlight not returning the expected results when searching Am I right to think that Spotlight or Finder should search through the contents of a file?

When I search in Finder or Spotlight for a word inside a text (.txt) or rtf document, it doesn't return anything.
Example: I have a simple rtf or txt file in Documents that contains the word "car".

Neither of these returns anything:
car
contains:car
kind:rtf contains:car
kind:txt contains:car
kind:text contains:car

the document has been there form weeks so it should have been indexed.

All spotlight settings are the defaults (everything selected).
I'm using Mojave in a Mac Mini 2014.

Any help welcome.
Fixed!.  I just rebuilt the spotlight index like this:
System preferences > Spotlight > Privacy, add and then remove the folder that wasn't returning the expected results (I did it with the home folder just to make sure all is indexed), after you quit System preferences the index will rebuild for that folder.  I guess you need to wait a bit for macOS to rebuild (5 minutes, 1 hour or more? I don't know, it surely depends on the size of the folder).