I didn’t think you could hold a firm and an unconditional together?
If an offer is unconditional if firmed a d you firm that university, you cannot have an insurance, as it is redundant. If the offer is just uncondituonal - and some universities do this, even pre-results - you can make it your firm with no insurance, or have it as a 'sure bet' I surancechoice.
Re telling a university that has rejected the student that their mock grades were higher than the final grades sent to UCAS and on to the university, one would assume that the first step would be to get the school to instigate an appeal, if it doesn't do that automatically, then tell the university that an appeal is in progress and therefore please will they keep the application under consideration, pending the result.
Universities have already been told that they are expected, wherever possible, to hold a place pending an appeal and this year, the deadline for fulfilling all conditions has been extended by a week, to 7th September.