Need to get my formula to check dates and use relevant one

I am trending study data and have results over a large time period however I only want to use the results in my formula that are with the specified date range (B6:B7).
My formulas trend the values where they meet the criteria to produce a date. However should this trended date be outside the date range B6:B7, I want to use the value to the point where it uses B6 if its value is <B6 and B7 where the value is >B7. Conversly Should it's value be >B6 or <B7 I want to use the value generated.

I have attached 2 examples of my problem and as usual any help is welcome and I thank you in advanced

Thanks

Gav