Need Equation that looks a 2 list of dates & select most current date that is Today or old

Need Equation that looks a 2 list of dates & select most current date that is Today or older

Here is a working equation that selects from 2 sheets in Excel and chooses most current date.
=MAX(LOOKUP(99^99,currentmonth!A:A/(currentmonth!B:B=A15),currentmonth!A:A),LOOKUP(99^99,mainlogbook!A:A/(mainlogbook!B:B=A15),mainlogbook!A:A))

unfortunately one of the sheets has future dates so it always grabs the most future date that is beyond today's date.
Is there a way to make this equation only select the latest date that is today or older?

Thanks

A quick thought would to have a separate column with a formula that will only display dates today and older, than have your formula reference that.

A sample file update will be helpful.