That is good news for you. I think RM will want to settle as cases like yours really highlight how unfair and “annoying” this 8 hour agreement is and so they will want to stop them going further and being joined with the current cases to be heard in April.
Just see what they offer and decide if you want to accept. The ACAS person will do all your talking. Good luck!
Hopefully other people who lost out in this backdated pay round will follow your example. If enough do, the criteria could well get changed going forward.