Don't reference LocalDate.now during getRequirements - defer date resolution using DateConstraint instances until execution time. Increase flexibility of the DateConstraint class. Explicitly reference NULL and NOW date evaluations. Remove redundant PERIOD from historical valuation constraints to avoid equivalence ambiguity - e.g. "Start=-P5Y,End=Now", "Start=-P5Y,Period=P5Y", "Period=P5Y,End=Now".
Unit test and fixes to DateConstraint.