Footnote marker hanging beside text (which is all flush left of table)

Question

I'm using the threeparttable package to produce footnotes directly beneath my table with the tablenotes environment. My regular footnotes (using KOMA-script) have the footnote marker hanging in the margin. I'd like the tablenotes to behave similarily, as shown below:

  some table with bottom rule
  ___________________________
1 Tablenote...

Another example:

I've Googled around and tried some stuff out by modifying some definitions in threeparttable.sty to no avail.

EDIT:

See MWE below.

\documentclass[11pt,
twoside=false,
letterpaper,
hidelinks,
parskip=half+,
%onehalfspacing,  % see setstrecj after \begin{document}
bibliography=numbered,
numbers=noenddot,
]{scrartcl}
%
\usepackage[para]{threeparttable}
\usepackage{booktabs}
\usepackage{footnotebackref}
\usepackage{tablefootnote}
%
\renewcommand{\TPTnoteSettings}{
    \renewcommand{\baselinestretch}{0.8}
    \setlength\leftmargin{0.0em}%
    \setlength\labelwidth{0.0em}%
    \setlength\labelsep{0.0em}%
    %   \rightskip\tabcolsep \leftskip\tabcolsep
}%
% http://mirror.las.iastate.edu/tex-archive/macros/latex/contrib/threeparttable/threeparttable.sty
% Attempted this///
%\def\tnote#1{\protect\TPToverlap{\makebox[0em][r]{\textsuperscript{\TPTtagStyle{#1}}}}}% TRYING TO REDEFINE THE tnote SO THAT IT IS GLUED TO THE LEFT SIDE... BUT THE PROBLEM IS THAT IT CHANGES FOR BOTH, also the notes are still indented slightly
%
% SO MY IDEA IS TO CHANGE THE SURROUND THE \tnote INSTANCE WITH A MAKE BOX AS IT APPEARS IN THE tablenotes environment
%
%but I get lost here
%\def\tablenotes{\TPT@defaults 
%   \@ifnextchar[\TPT@setuptnotes\TPTdoTablenotes} % ]
%\let\endtablenotes\endlist
%\def\TPT@setuptnotes[#1]{% process formatting options
%   \@for\@tempa:=#1\do{\@nameuse{TPT@opt@\romannumeral-`a\@tempa}}%
%   \TPTdoTablenotes
%}
%%
%\def\TPTdoTablenotes{%
%   \par \prevdepth\z@ \TPT@hsize 
%   \list{}{\topsep\z@skip \partopsep\z@skip 
%       \itemsep\z@ \parsep\z@ \itemindent\z@
%       \TPTnoteSettings
%       \let\makelabel\TPTnoteLabel
%}}
%
% so I figured I'd try to change how it is done in para mode
% I cant seem to get it working here also
\def\TPT@opt@para{\let\TPTdoTablenotes\TPT@doparanotes}
\def\TPT@doparanotes{\par
    \prevdepth\z@ \TPT@hsize
    \TPTnoteSettings
    \parindent\z@ \pretolerance 8
    \linepenalty 200
    \renewcommand\item[1][]{\relax\ifhmode \begingroup
        \unskip
        \advance\hsize 10em % \hsize is scratch register, based on real hsize
        \penalty -45 \hskip\z@\@plus\hsize \penalty-19
        \hskip .15\hsize \penalty 9999 \hskip-.15\hsize
        \hskip .01\hsize\@plus-\hsize\@minus.01\hsize 
        \hskip 1em\@plus .3em
        \endgroup\fi
        \makebox[0em][r]{\tnote{##1}\,\ignorespaces}%
    \let\TPToverlap\relax
    \def\endtablenotes{\par}%
}
\begin{document}
%
\begin{table}[tbph]
    \begin{threeparttable}[t]
    \centering
    \begin{tabular}{lccc}
    \toprule
    Line 1\tnote{a}      & 630.0                           &                                 & 65.0 \\
    Line 2\tnote{b}                        & 251.0                           &                                 & 64.0 \\
    \midrule
    Total                           &                                 &                                 &  \\
    \bottomrule
    \end{tabular}%
    \begin{tablenotes}\footnotesize
        \item[]Some note without a number \\ Multiline\\
        \item[a]M Another \\ Multiline\\
        \item[b] A run on long long long line that extends past the table
        \item[1] One same; \item[2] line
    \end{tablenotes}
\end{threeparttable}
\end{table}%
%
\end{document}

Answer 1

In {NiceTabular} of the latest version of nicematrix (5.0 of 2020/07/15), you have a command \tabularnote and the notes are composed at the end of the tabular with a type of list of enumitem. All the options provided by enumitem are available to customize that list.

\documentclass[11pt]{scrartcl}

\usepackage{booktabs}
\usepackage{nicematrix}
\usepackage{enumitem}

\begin{document}

\NiceMatrixOptions 
  {
    notes = 
     {
       code-before = \footnotesize ,
       enumitem-keys = 
        {
          labelsep = 1 mm , 
          labelwidth = 2 cm ,
          leftmargin = 0 pt ,
          align = right ,
        }
     }
  }

\begin{table}[tbph]
    \centering
    \caption{My table}
    \begin{NiceTabular}{lccc}
    \toprule
    Line 1\tabularnote{A very very very very very very very very very very very very  long note} & 630.0 & & 65.0 \\
    Line 2\tabularnote{A long note but not as long as the previous one} & 251.0 & & 64.0 \\
    \midrule
    Total & & &  \\
    \bottomrule
    \end{NiceTabular}%
\end{table}%

\end{document}