..... ISTR recall that the RAF opted me out of SERPS very many years ago = pre 1977 ....
My understanding is that SERPS didn't start until April 1978. Prior to that there was Graduated Pension, and since April 2002 SERPS was replaced by the Second (or Additional) State Pension. Having recently requested and received a State Pension Statement (forecast), the calculations and rules seem fiendishly complicated, especially when taking account of some periods that were 'contracted out', and others that were not!