@Phssthpok: What you think!? I am a hard working man ...

... the book is already nearly finish. I found out what stand the problematic entities for (numbers and some characters) and did S&R. Unluckily, so I lost the small caps characters: e.g.  appears as normal Unicode N (U+004E).
Then later, I thought, I will correct this, so to speak, self-produced error manually. This is, of course, unprofessional (I hate unprofessionalism). Additionally make possibly overseeing to transform some of the former small caps.
Luckily, before I touch new books for editing I make original copies. So I am able to process your suggestions now:
I merged all Files Browser entries (3.9 MB), then did the instructions in
#4 (I didn't have to create the function again, it's stored under
Phssthpok). You are linked with
''problematic Unicode'' 
Replace all: 3.900.000 ocurrences! So I hadn't to do point 8) and 9) of the instructions: the book is full of that stuff.
New problematik: C&P your example
 doesn't work (Error: Not found). I had to find such a character in the book and C&P that one to the Find-box. Here it is: -
apparently the same!
Now I thought for @Terisa de morgan (#9): can not be ...
''clear and crystalline for everybody to understand''
Find: <span class="small-cap">(.*?)</span><span class="small-cap">
Replace: <span class="small-cap">\1 ... must be
Find: <span class="small-cap">(.*?)</span>
Replace: <span class="small-cap">\1</pan>
Your help was tremendously valuable. I wouldn't have managed that in years. Especially not so professional.