You will always have one file for each month you have used a particular version of MC, plus up to ten files for the current and previous months.
So if you had 15 years of library backups on the one version of MC, you would have about 200 files, and 1GB of data. Not worth worrying about.
There are no parameters to change this arrangement. You could use an external tool to delete old backups if you wished, and even automate it.