I'm going to give up on extracting everything and want to try only extracting the files which have not yet been extracted and putting them into the correct subfolder (which is D:\Some\Specific\Folder\Archive\yyyy\mm\dd\ - based on the date in the filenames ; these folders already exist). All this using 1 little Perl-script so I can just start it up and let it run as long as it needs to without having to worry about it anymore until it's done.

# !perl

use strict; # because we should
use warnings; # because we should

my $base = 'D:\Some\Specific\Folder\Archive\\';

# This might hurt your eyes, but for some obscure reason, DateTime is 
+not installed and I can seriously not be bothered to install it mysel
+f
my @years = ('2011','2012','2013','2014','2015','2016','2017');
my @months = ('01','02','03','04','05','06','07','08','09','10','11','
+12');
my @days = ('01','02','03','04','05','06','07','08','09','10','11','12
+','13','14','15','16','17','18','19','20','21','22','23','24','25','2
+6','27','28','29','30','31');

my $archive = glob qq($base.Gridfee0?.7z\\);
    #Tried glob qq($base.Gridfee0?.7z\\Gridfee*\\) and glob qq($base.G
+ridfee0?.7z) too, same result

foreach my $year (@years)    {

    foreach my $month (@months)    {
    
        foreach my $day (@days)        {
            
            my @files = glob qq($base\\Gridfee0?.7z\\Gridfee?\\invoic_
+b2c_$year$month$day*.txt);
                # The zipfiles are zipped folders, so there is 1 extra
+ layer to traverse, hence the \\Gridfee?\\
                # The name is definitely correct: for example Gridfee0
+5.7z contains folder named Gridfee5
                # But possibly made a mistake in the syntax?
                
            foreach my $file (@files)    {
                
                my $extdir = '-o $base.$year\$month\$day\\';

                system ('C:\Program Files\7-Zip\7z.exe',' e ',$archive
+,' -r',$extdir,$file,' n n') or die $!;
                    # Many things in Perl are a mystery to me and the 
+use of 7z via Perl is most definitely one of them
                    # This is the syntax I have distilled from what in
+fo I could find on interaction between Perl and 7z
                    # and from the 'Help'-file that comes with the 7zi
+p-program
                    # The ' n n' is my attempt at making 7zip skip the
+ files which can already be found in $extdir
                
                    say('Moved '.$file.' to '.$extdir);
                        # Just a check to see what has been done, if a
+nything
            }
        }
    }
}

exit 0;
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