Ginsing,
I believe Biggus is right, If "I" retire at 50 (on the PA spine)
having joined at 16 my EDP is based on 50% of preserved pension at 40 plus 10 times 1.66 (call it a total of 66% of preserved pension). At 55 my EDP is increased to 75% of my preserved pension plus RPI....At 65 I get my pension plus the "other lump sum"....Thoughts?