Character/word counting implementation must handle externalized content called via \input{}

Question

This helpful implementation (for which we're grateful) may lack the ability to count characters or words contained within externalized content. As an example, please see this mwe.

The code is currently not compiling on my systems. I wonder if it possible there is a conflict with filecontents. Regardless, we would like to be able to count both externalized content as well as bib items which may appear in a refsection.

\documentclass{article}
\usepackage{tokcycle}[2021-03-10]
\usepackage{xcolor}
\newcounter{wordcount}
\newcounter{lettercount}
\newcounter{wordlimit}
\newif\ifinword
% USER PARAMETERS
\newif\ifrunningcount
\newif\ifsummarycount
\def\limitcolor{red}
\setcounter{wordlimit}{0}
%%
\makeatletter
% \tc@defx is like \def, but expands the replacement text once prior to assignment
\newcommand\addtomacro[2]{\tc@defx#1{#1#2}}
\newcommand\changecolor[1]{\tctestifx{.#1}{}{\addcytoks{\color{#1}{}}%
  \tc@defx\currentcolor{#1}}}
\makeatother
\newcommand\dumpword{%
  \addcytoks[1]{\accumword}%
  \ifinword\stepcounter{wordcount}
    \ifrunningcount\addcytoks[x]{$^{\thewordcount,\thelettercount}$}\fi
    \ifnum\thewordcount=\value{wordlimit}\relax\changecolor{\limitcolor}\fi
  \fi%
  \inwordfalse
  \def\accumword{}}
\newcommand\addletter[1]{%
  \tctestifcatnx A#1{\stepcounter{lettercount}\inwordtrue}{\dumpword}%
  \ifcountspaces\tctestifcatnx .#1{\stepcounter{lettercount}}{}\fi% NEW!!
  \addtomacro\accumword{#1}}
\newif\ifcountspaces% NEW!!
\xtokcycleenvironment\countem
  {\addletter{##1}}
  {\dumpword\groupedcytoks{\processtoks{##1}\dumpword\expandafter}\expandafter
    \changecolor\expandafter{\currentcolor}}
  {\dumpword\addcytoks{##1}}
  {\dumpword\ifcountspaces\stepcounter{lettercount}\fi\addcytoks{##1}}% NEW!!
  {\stripgroupingtrue\def\accumword{}\def\currentcolor{.}
    \setcounter{wordcount}{0}\setcounter{lettercount}{0}}
  {\dumpword\retainsum\ifsummarycount\tcafterenv{%
    \par(Wordcount=\thewordcount, Lettercount=\thelettercount)}\fi}
\newcommand\contentlimit[1]{\setcounter{wordlimit}{#1}}
\newcounter{globalwordcount}
\newcounter{globallettercount}
\newcommand\retainsum{%
  \addtocounter{globalwordcount}{\thewordcount}%
  \addtocounter{globallettercount}{\thelettercount}%
}
\newcommand\processCount{\ifnum\thegloballettercount>0%
  \par Global Wordcount=\theglobalwordcount\
  Global Lettercount=\thegloballettercount
\fi}
\newcommand\disablecountem{\let\countem\empty\let\endcountem\empty}
\begin{filecontents}{externalized_content.tex}
Here is some externalized content!
\end{filecontents}
\begin{document}
%\disablecountem% TO TURN OFF COUNTING, WITHOUT CHANGING DOCUMENT
\section*{Over the Limit}
\contentlimit{5}\countem
This content is over the limit.
\endcountem
\section*{Externalized content}
\contentlimit{2}\countem
\input{externalized_content.tex}%
\endcountem
\section*{Example of also counting spaces and punctuation}
\countspacestrue% NEW!!
\countem
x! , ;x\endcountem
\section*{Document analysis}
\processCount
\end{document}

Best