CH/0392/2009 concerned the date of claim and start date of entitlement in a pensioner CTB case; it’s the closest I can think of to your issue. It sets out how the date of claim is decided, at that time 12 months before the date the claim was made in certain circumstances, by reference to regs 53(1ZA), 56, and 48 CTB(SPC) Regs 2006. Admittedly it concerned an argument over whether February 2007 or July 2006 was the correct date to use.
At para 33 Judge Jacobs said that the earliest date of entitlement is set by regs 53(1ZA) and 56, then in para 34 that the actual effective date is set by reg 48: “it is the first day in the benefit week following the first day in respect of which the claim was made. The claimant may specify a date from which the claim is made. If so, that is the effective date, provided the other conditions of entitlement are satisfied. If the claimant does not specify a date, the LA has two choices. It may ask the claimant to specify a date. Or it may take the most favourable date, which is the maximum of [12] months. In this case, we know that the claimant wanted to claim CTB from 2005.”
Reg 48 CTB(SPC) Regs is, as far as I can see, more or less matched by reg 57 HB(SPC) Regs 2006, so I think the combined effect of that and the UT decision allows you to use the date the claimant asked for. Although the CTB(SPC) Regs have now been repealed I think reg 57 HB(SPC) Regs is similar, but I might be wrong.