Thank you all very much! @Jon/T, brilliant suggestion.
I opened one exported .enex file in my text editor, counting <note>, <created> and <title> they were all 33, which was the number exported and imported. But one has the title "Untitled Note" (original title DIY Tips), the contents of the notes are 100%, just no title:
<title>Untitled Note</title>
<created>20190328T170508Z</created>
<updated>20230505T222609Z</updated>
<note-attributes>
<author>Me</author>
</note-attributes>
<content>
</content>
<resource>
<data encoding="base64"></data>
<mime>image/png</mime>
<width>225</width>
<height>225</height>
<resource-attributes>
<file-name>image.png</file-name>
<source-url></source-url>
</resource-attributes>
</resource>
</note>
Looking at the 3 untitled notes (1 in this notebook) mentioned, 2 contain resources, e.g.:
![[./_resources/Untitled_Note.resources/image.png]]
[[./_resources/Untitled_Note.1.resources/nov 11 1.jpg]]<
but not the 3rd.