average sales per month

For this, I would try to contact Adobe directly instead of using this mostly user to user forum with some Adobe participation. I never looked into Adobe's earning reports, but if there is public information available, it will be in those earning reports.

Only Adobe could know, and there is no chance they would reveal such commercially sensitive information. And what would you mean by average: licenses or revenue? Mean, mode or median? Total or per contributor? Adobe's income or contributor income? In what country and currency? Etc