Answer by egreg for Find the highest year in a string

I'd go with expl3 all along.

\documentclass{article}\ExplSyntaxOn\NewDocumentCommand{\primarySection}{O{primary}mmmmm} {  \__sky_year_extract:n { #5 }  \int_compare:nTF { \c_sys_year_int - 5 > \l__sky_year_recent_int }   % replace the two following branches   { not~recent~year~(\int_use:N \l__sky_year_recent_int) }   { recent~year~(\int_use:N \l__sky_year_recent_int) } }\int_new:N \l__sky_year_recent_int\seq_new:N \l__sky_year_all_seq\cs_new_protected:Nn \__sky_year_extract:n {  \regex_extract_all:nnN { [0-9]{4} } { #1 } \l__sky_year_all_seq  \seq_sort:Nn \l__sky_year_all_seq   {    \int_compare:nNnTF { ##1 } > { ##2 } { \sort_return_same: } { \sort_return_swapped: }   }  \int_set:Nn \l__sky_year_recent_int { \seq_item:Nn \l__sky_year_all_seq { 1 } } }\ExplSyntaxOff\begin{document}\primarySection  {Data 1}   {Data 2}  {Data 3}  {Jan. 1930 - June 2023} % Dates  {Data 4}\primarySection  {Data 1}   {Data 2}  {Data 3}  {Jan. 1930 - June 2001} % Dates  {Data 4}\end{document}

Since I can't make a sense out of your \secondarySection macro (you end up with exactly the same tokens in both cases), I replaced it with code that shows what branch is taken.