Yes individual items on the programme should have had TRA considered and demonstrated in case they become critical and to demonstrate that it is a practical realistic programme. It is not only the critical path that should consider TRA, as you have demonstrated critical paths have a (nasty) habit of changing!
A Contractor can change items on the programme during the project which could be to increase TRA that they previously though was missing or light, but you will have a hard job getting that agreed if you suddenly do it to an item that is now becoming critical.
A Contractor can change items on the programme during the project which could be to increase TRA that they previously though was missing or light, but you will have a hard job getting that agreed if you suddenly do it to an item that is now becoming critical.