I'm confused about what you're trying to do.
Why not just zip the entire directory? The zip process doesn't care if there were 10 files yesterday, and 10 new ones that it added today.
Create a batch file that deletes yesterday's zip file, then creates a new one for today.
Create a batch file that archives the *.wek files one at a time. If the archived file already exists, don't do anything to that file.
Code for Option 3:
:: This file will backup *.wek files into *.wek.zip
:: i.e., abc.wek gets zipped into abc.wek.zip
:: If the matching zip file already exists, the original file does not get backed up.
:: i.e., if cde.wek.zip already exists, then cde.wek does not get backed up
:: change \path\to\files (below) to the correct path to your files that need to be backed up
:: change \path\to\archives (below, twice) to the correct location of your backup folder
:: change c:\tools\7zip\7za.exe (below) to the correct path to the 7-zip command-line tool
:: make sure we're on the C drive
:: change to our data directory
:: create the backups
for %%k in (*.wek) do if not exist "c:\path\to\archives\%%k.zip" c:\tools\7zip\7za.exe a "c:\path\to\archives\%%k.zip" "%%k"