Doesn't Devonsphere search indexed files in Devonthink?

My database in Devonthink says 17,000 files.
DevonShephere has found only about 3000 of them.

Why?

Which search term and which edition of DEVONthink do you use?

I am using the latest Devonthink Pro office (2.9.16), and the latest DevonShere express.

Why do you ask me about the term?
If the items are not indexed, does it matter what search terminology I use?

Probably, I don’t understand on how these two applications communicate their databases.

The number of results depends on the search term (and in case of DEVONthink on the search settings). In addition, is the Spotlight index of all databases in DEVONthink (see File > Database Properties) enabled?