如何将多个表格注释放入一个单元格中？

Question

我一直在尝试整理表格。由于表格会很长，所以我在这里使用了 longtable，但对于较短的表格，问题也是一样的。

我想在表格中的某些行添加一些注释，为此我使用了-packageThreePartTable提供的环境threeparttablex。现在的问题是表格注释本身直接打印在文本后面，不会占用空间，这通常很好，因为它不会改变对齐方式。但如果我需要对同一个单元格添加两个注释，则两个字母会打印在彼此的顶部。有一种糟糕的解决方法，使用上标并手动添加空格，但看起来一点也不好看。我现在的问题是：是否有可能以更好的方式做到这一点？

两种情况下的 MWE 如下：

\documentclass{article}
\usepackage{threeparttablex}
\usepackage{longtable}
\usepackage{booktabs}

\begin{document}

\begin{ThreePartTable}
    \begin{TableNotes}
        \item[a] Reaction was performed according to GP1
        \item[b] Reaction was performed according to GP2
        \item[c] Alkynol XX was used
    \end{TableNotes}

    \begin{longtable}{ccc}
        \caption{table without workaround}\\    
        \toprule
        reagent & additive & temperature\\
        \midrule \endfirsthead
        %
        reagent & additive & temperature\\ 
        \midrule \endhead
        %   
        \bottomrule
        \insertTableNotes\\
        \endlastfoot
        %       
        reagent1\tnote{a} & --- & r.t.\\
        reagent2\tnote{b} & --- & cold\\
        reagent3\tnote{b}\tnote{c} & stuff, which didn't work & warm\\
    \end{longtable}
\end{ThreePartTable}

\begin{ThreePartTable}
    \begin{TableNotes}
        \item[a] Reaction was performed according to GP1
        \item[b] Reaction was performed according to GP2
        \item[c] Alkynol XX was used
    \end{TableNotes}

    \begin{longtable}{ccc}
        \caption{Table with manual space and comma}\\   
        \toprule
        reagent & additive & temperature\\
        \midrule \endfirsthead
        %
        reagent & additive & temperature\\ 
        \midrule \endhead
        %   
        \bottomrule
        \insertTableNotes\\
        \endlastfoot
        %       
        reagent1\tnote{a} & --- & r.t.\\
        reagent2\tnote{b} & --- & cold\\
        reagent3\tnote{b}\ $^,$\tnote{c} & stuff, which didn't work & warm\\
    \end{longtable}
\end{ThreePartTable}

\end{document}