Mistaken new PIP claim instead of MR

Client 2 points short of a SDL component award so social worker was going to request MR. Meanwhile support worker made a new claim. Would any success at MR only hold until the date of the new claim whereupon the decision on the new claim would prevail?

Once the appeal has been decided the claimant can ask DWP to take that decision into account when deciding the new claim. Or if the new claim has already been decided (and is less favourable than the appeal decision) s/he can ask DWP to revise that decision taking the new information into light.
UC (DA) 2013 regs 11(2).

If DWP refuses, the claimant can appeal the decision on the new claim, and use the previous appeal decision as supporting evidence (assuming current conditions/effects are broadly similar).

EDIT: typos

Many thanks for that. Very helpful,