Ex Cathedra
That will be your only defence, i.e. I wanted RA65 when the company offered it in April 2009 but the significant pay cut required to change contracts was unacceptable to me and my family and I told the company this in a signed letter sent to them on the 30th April 2009.
FOCX
Not offering you RA65 is discrimination. Offering you a contract with RA65 but on lower pay that starts the day the contract starts is industrial bustardry but isn’t discrimination. You could argue though that it is discrimination if the pay cut occurred on you 55th birthday.