I am not sure if you are looking to do the same case in the where clause to compare the product and order load date with the start and end date

where loaddate between @Start and @END

the above where can be written as

loaddate >= @Start and loaddate<= @END

the below query migt be help for you , but if u could provide exact requrment with the sample data and the table structure , could help in writing

where @END>loaddate and @Start<loaddate

where @End >=

CASE WHEN a.loadate >= b.loaddate

THEN a.loaddate

ELSE b.loaddate

END

and

@Start <=

CASE WHEN a.loadate >= b.loaddate

THEN a.loaddate

ELSE b.loaddate

END