I like that.
The garage is fully entitled to stop offering Polos to new customers.
But if they have offered the customer who bought the Passat a contractual right to a Polo after 12 months, then they must offer a Polo.
Of course, the garage could have written to original contract as follows: " At the end of the 12 months, you can choose from a Polo, a Passat or a Touareg - provided we are still offering those models to new customers".
Then the garage would have been fully entitled not to offer the Polo.
Likewise, if AIB had said, "You will be offered a tracker mortgage at the prevailing rate, provided that we are still offering tracker mortgages to new customers.", then AIB would have been entitled not to offer you a tracker on expiry of the fixed rate.
Brendan