retrospective-12 years ago-assessments-how comes?

Is it really possible and what rights does the tax payer have where an inspector to makes a "with hindsight" assessment based on recently amended tax rules(film partnerships losses) for a case/claim 12 years ago;  

this is ridiculously unfair when under new rules the department will only go back four years where you request am amended assessment under an overpayment relif claim!!!!!!!!!!!!!!!!!!! w rules

Have the cake and eat it and give the "customer"/taxpayer a cherry to suck!!!!!