I just spotted another example where one could get rid of at
least two files by creating a generic Open !CHM!DJVU!EPUB!.BAT

@echo off
:: chm.bat -- Opens CHM file using open source, portable SumatraPDF-3.2-64.exe
:: https://www.sumatrapdfreader.org/free-pdf-reader.html
:: Reads PDF, eBook (ePub, Mobi), XPS, DjVu, CHM, Comic Book (CBZ and CBR)
start "" C:\1\SumatraPDF-3.2-64.exe %1

@echo off
:: djvu.bat -- Opens DJVU file using open source, portable SumatraPDF-3.2-64.exe
:: https://www.sumatrapdfreader.org/free-pdf-reader.html
:: Reads PDF, eBook (ePub, Mobi), XPS, DjVu, CHM, Comic Book (CBZ and CBR)
start "" C:\1\SumatraPDF-3.2-64.exe %1

@echo off
:: epub.bat -- Opens EPUB file using open source, portable SumatraPDF-3.2-64.exe
:: https://www.sumatrapdfreader.org/free-pdf-reader.html
:: Reads PDF, eBook (ePub, Mobi), XPS, DjVu, CHM, Comic Book (CBZ and CBR)
start "" C:\1\SumatraPDF-3.2-64.exe %1

If I ever need to read CBZ or CBR content, I would just rename
the file, no need to edit its contents:

!CHM!DJVU!EPUB!CBZ!CBR!.BAT