How to find glyphs in pdf requiring \pdfglyphtounicode to allow validation?

Question

This question continues one begun in commments to https://tex.stackexchange.com/a/551291/13492.

The issue:

To determine all those glyphs in pdf output, as from the MWE below, that are preventing pdf validation (under standard PDF a 2-u). Namely, because the file fails the rule "The Font dictionary of all fonts shall define the map of all used character codes to Unicode values, either via a ToUnicode entry, or other mechanisms as defined in ISO 19005-2, 6.2.11.7.2."

The two commands\pdfcompresslevel=0 and \pdfobjcompresslevel=0 cause the output from pdflatex to be a readable, pure-ASCII file.

The question:

What do I look for in the ascii pdf so as to subsequently include a suitable \pdfglyphtounicode command?

If I process the file with pdflatex first, as it is shown, and then again but with the two lines

    \pdfglyphtounicode{summationdisplay.1}{0060 0060 0060 0060 0060 0060 0060 0060}%
    \pdfglyphtounicode{summationdisplay}{0060 0060 0060 0060 0060 0060 0060 0060}%  

commented out, and if I then examine the resulting ascii pdfs, the only substantial difference I detect is:

• with those two lines included in the source, the pdf includes once the line

  dup 213 /summationdisplay.1 put

and then the line:

/CharSet (/radicalBigg/radicalbig/radicalbigg/summationdisplay.1/uni222B.dsp)

• with those two lines commented out, the pdf includes dup 213 /summationdisplay.1 put twice but does not include /CharSet (/radicalBigg/radicalbig/radicalbigg/summationdisplay.1/uni222B.dsp).

Erroneous inference:

From the above, I'm tempted to infer that I will need to include \pdfglyphtounicode commands in the source for glyph names occurring in pdf file lines of the GREP form

dup [0-9]+ /\S+ put

But that surely is not correct! After all, the pdf file includes many such lines, for example:

dup 149 /period put
dup 48 /u1D44E put
dup 49 /u1D44F put
dup 150 /comma put
dup 56 /u1D456 put
dup 58 /u1D458 put
dup 115 /radicalBigg put
dup 112 /radicalbig put
dup 114 /radicalbigg put
dup 213 /summationdisplay.1 put
dup 185 /uni222B.dsp put
dup 61 /equal put
dup 8 /uni03A6 put
dup 33 /arrowright put
dup 49 /infinity put
dup 0 /minus put
dup 184 /plus put
dup 6 /plusminus put
dup 112 /radical put
dup 33 /A put
dup 34 /B put
dup 40 /H put
dup 41 /I put
dup 42 /J put
dup 43 /K put
dup 50 /R put
dup 52 /T put
dup 65 /a put
dup 66 /b put
dup 67 /c put
dup 12 /comma put
dup 68 /d put
dup 69 /e put
dup 1 /exclam put
dup 70 /f put
dup 20 /four put
dup 71 /g put
dup 72 /h put

The MWE:

\documentclass{article}
% To examine pdf as pure ASCII:
\pdfcompresslevel=0
\pdfobjcompresslevel=0
\usepackage{hyperxmp}
\RequirePackage[type={CC},modifier={by-nc-nd},version={4.0},lang={english}]{doclicense}
 \usepackage[pdfa]{hyperref}
   \hypersetup{
      pdfapart=2, pdfaconformance=u,
      bookmarksnumbered,
      pdftitle={A Book}, pdfauthor={Anonymous}, pdfcreator={somebody},
      pdfsubject={A general introducton to things}, pdfkeywords={things, stuff},
      pdflicenseurl={http://creativecommons.org/licenses/by-nc-nd/4.0/}
    }%
    \input{glyphtounicode}
    \pdfgentounicode=1
    \pdfglyphtounicode{EM}{0058 0058 0058 0058 0058 0058 0058 0058}%
    \pdfglyphtounicode{NUL}{0060 0060 0060 0060 0060 0060 0060 0060}%
    \pdfglyphtounicode{uni222B.dsp}{222B}%
    \pdfglyphtounicode{summationdisplay.1}{0060 0060 0060 0060 0060 0060 0060 0060}%
    \pdfglyphtounicode{summationdisplay}{0060 0060 0060 0060 0060 0060 0060 0060}%

    \pdfglyphtounicode{radicalBigg}{0060 0060 0060 0060 0060 0060 0060 0060}%
    \pdfglyphtounicode{radicalbig}{0060 0060 0060 0060 0060 0060 0060 0060}%
    \pdfglyphtounicode{radicalbigg}{0060 0060 0060 0060 0060 0060 0060 0060}%
    \immediate\pdfobj stream attr{/N 3} file{sRGB.icc}
    \pdfcatalog{%
        /OutputIntents [
         <<
             /Type /OutputIntent
             /S /GTS_PDFA1
             /DestOutputProfile \the\pdflastobj\space 0 R
             /OutputConditionIdentifier (sRGB)
             /Info (sRGB)
          >>
      ]
    }
\newcommand\mytitle{A Book}
\newcommand\myauthor{Anonymous}
\newcommand\myabstract{An introduction to things in general.}
\newcommand\mydate{\today}
\title{\mytitle}
\author{\myauthor}
\date{\mydate}
\usepackage{newtxtext,newtxmath}
\usepackage[french,ngerman,russian,main=english]{babel}
\usepackage{blindtext}
\begin{document}
abc abc
\maketitle
\blindmathpaper
\end{document}

Commnent:

The source here is just for experimentation. My real, book-length, document has a pdf ascii output file over a quarter-million lines long! Which is why I need help in what to look for (and what to do about it).

Related:

https://tex.stackexchange.com/a/551291/13492

How to find the proper glyph name required by \pdfglyphtounicode

How are the glyph (character) names in PDF-files determined?

How to fix missing or incorrect mappings from glyphtounicode.tex