I’m pretty sure that it is only one year’s award remaining and not three as it used to be.
From Motability website:
“According to the Scheme guidelines, you need to have at least 12 months remaining on your award to join the Motability Scheme. If you have less than 12 months remaining, you will not be able to place a new application until the Department for Work and Pensions extend or renew your allowance.”