Deferred pension

According to the DWP Decision Makers Guide:

For periods of deferment beginning on or after 6.4.05, the rate of RP is increased by 1/5% of the weekly rate of RP that would have been payable for every incremental period had entitlement not been deferred.

This seems to mean that the monetary increments are added together, and then added to what the undeferred pension would have been at the time of the claim.
The table above shows these increments.

Total increment is 864+881+895+912+940+963+992+1008+1040+1144+1234+368 = £11241.
So pension now would be 12234+11241 = £23475.

A year ago the increment would have been 864+881+895+912+940+963+992+1008+1040+1144+356 = £9995.
And the pension a year ago would have been 11863+9995 = £21858.
The triple lock increase for 2025 would increase this to 21858*1.0313 = £22542.

According to an expert on this BBC web page:

Your pension a year ago £21858 gross. Unless you claim the pension late in a tax year, the lump sum from backdating will likely all be taxed (you don't get a backdated personal allowance!). So you would probably get a net lump sum of 21858*0.8 = £17486.

With the 2025 triple lock increase the pension would become 21858*1.0313 = £22542 gross, which is £20548 net.
With a life expectancy of 16 years, you would get a total of 17486 + 20548*16 = £346254 net.

If you don't backdate, your pension now would be £23475 gross, which is £21294/year net.
With a life expectancy of 16 years, you would get a total of 21294*16 = £340704 net.

So if you backdate you would get 346254-340704 = £5550 more in total, but your net pension would be reduced by 21294-20548 = £746/year.
As a cross check: 17486-746*16 = 5550.

Your pension a year ago would have been £24569 gross. Unless you claim the pension late in a tax year, the lump sum from backdating will likely all be taxed (you don't get a backdated personal allowance!). So you would probably get a net lump sum of 24569*0.8 = £19655.

With the 2025 triple lock increase the pension would become 24569*1.0313 = £25338 gross, which is £22784 net.
With a life expectancy of 16 years, you would get a total of 19655 + 22784*16 = £384199 net.

If you don't backdate, your pension now would be £26611 gross, which is £23803/year net.
With a life expectancy of 16 years, you would get a total of 23803*16 = £380848 net.

So if you backdate you would get 384199-380848 = £3351 more in total, but your net pension would be reduced by 23803-22784 = £1019/year.
As a cross check: 19655-1019*16 = 3351.

If you don't backdate, your pension will be about £23475/year gross £21294/year net, which is 21294-14711 = £6583/year greater than mine, or £105328 over 16 years. To balance our incomes, you could transfer 105328/2 = £52664 to me.

If you backdate, your pension will be about £22542 gross £20548/year net, which is 20548-14711 = £5837/year greater than mine, or £93392 over 16 years. To balance our incomes, you could transfer 93392/2 = £46696 to me.
You would also get a lump sum of £17486 for the backdated year. So total to transfer to me would be 46696+17486/2 = £55439.

If you don't backdate, your pension will be about £26611/year gross £23803/year net, which is 23803-14711 = £9092/year greater than mine, or £145472 over 16 years. To balance our incomes, you could transfer 145472/2 = £72736 to me.

If you backdate, your pension will be about £25338 gross  £22784/year net, which is 22784-14711 = £8073/year greater than mine, or £129168 over 16 years. To balance our incomes, you could transfer 129168/2 = £64584 to me.
You would also get a lump sum of £19655 for the backdated year. So total to transfer to me would be 64584+19655/2 = £74412.