HPS is under-funded so any transfers out are valued pro-rata to the current level of funding in order to not leave the scheme worse off relative to the liabilities. Each valuation of the scheme published in the company annual reports (we haven't see HPS trustees version of the numbers for several years) shows the liabilities growing somewhat faster than the rate of inflation. One factor may be the upward adjustment of life expectancy but another factor will be reduced investment returns while the rate of pension increases is fixed. HPS (and all the other under-funded pension schemes) needs the central bankers to get inflation back to 5% or more!
The estimate of retirement benefits, however, assumes that the money will be there, in the fullness of time, to pay the pensions.