I'm surprised that I seem to be the first one to suggest a Schwartzian Transform:

@TXT = map { s/\d+ //; $_ }
       sort
       map { s/(.*?)_(\d+)_/sprintf("%04d %s_%s_",$2,$1,$2)/e; $_ } gl
+ob( "*.txt" );
[download]

(Not fully tested, but updated to add a missing "_" in the replacement string of the s///e operation)