hahaha… It doesn’t actually require that but to answer your question i would add a field called every for the day of the month and day of the week. So every 3rd Tuesday, etc. Bet again, not a concern right now or in the foreseeable future. And I can see how if one needs to cover every combination that would be pretty complex. At least more so than what I am doing.
So you’re smarter than I am, how would you lay this out. I know in the past I have a tendency to try to “help” the database and more often than not get chastised to let it do it’s thing. It will do it better than I can. 
So am I overthinking this?