I'm not sure. Try the bord_RecDescriptor field in Custom_Tables for your custom entities 

Getting an error when replying.

Nice try Matthew.  When I looked at that field I thought you had hit the nail on the head.  Some other tables have data in there that are consistent with the Quickfind results - eg the Quotes table has:

#Quot_Reference#:#Quot_Description#

which corresponds with the Quickfind results for quotes.

In the CRM\<Instance>\QuickFind\instance\conf\data-config.xml file the query for Quotes is clearly consistent with the bord_RecDescriptor value.

The value of bord_RecDescriptor for my custom entity was NULL.  When I changed it to a field with data (surounded by # symbols), it made no difference to the results.  I also refreshed metadata, stopped the QuickFind service, deleted the Quickfind folder and restarted the Quickfind service.  The Quickfind folder is re-created.  In data-config.xml, the query for my custom entity is unchanged, ie it still wants to index the <enty>_Name field and not the field I set in bord_RecDescriptor.

One thing I noticed about the newly created Quickfind\instance\conf files is the file date stamps.  Most of them are dated 31/01/2020 (I'm using CRM 2020 R1) but the data-config.xml is dated 21/03/2021 (ie yesterday).  This suggests to me that the file is being copied from somewhere rather than being generated anew (otherwise it would have today's date) but I haven't managed to figure out where from yet.  If I can find the source file I can try amending the query directly.

When I include the SELECT query in my post, it causes an error.

The only other thing I can think of is to check the Translations and look up a family called 'SS_ViewFields' and the Code would be the name of your custom entity. 

Thanks Matthew.  I've already done that - made no difference.

Well, some sort of hidden magic has happened.  When I re-visited this problem this morning with the intention of adding a TLS to copy the data I need to display in the Quickfind results to the <enty>_Name field, I found that it was working using the field I had added to Bord_RecDescriptor.

The only thing I can think of that may have spurred it into action is I changed the Bord_IsIndexed field from 'y' to 'Y'.  I was clutching at straws at that point but all other indexed entities had it set to 'Y' (ie capitalised) so I changed it.

I've found that I can now change the content of Bord_RecDescriptor, restart the CRM Quickfind service and a few minutes later the Quickfind results list reflects the changes.

Great news, you were having me scratching my head on that otherwise 

Could be a bit like Mail Merge fields, if you add a new field to a merge view, for some reason you have to restart TomCat in order for it to merge data in the Word/PDF document (even though you can query the view and the data is there)