Are asking a SQL question or a CR question?  If it is a CR question, for #1 you can't in a formula.  If you group by pay date records ascending, then the last group with have the latest dated record.  #2 I believe you can create a formula using the dateadd function that will achieve what you want (it have to be a record selection formula), Something like this {someDatefield} >= dateadd"yyyy",{?dateparm1},-1) and {someDatefield} <= dateadd("yyyy",{?dateparm2",-1}.

I hope this helps.