Ms. Houghton may be mistaken; we have no way of knowing.
The 'existence of two versions of a birth certicate', each one 'containing different dates of birth', with 'around about a 3 months conflict' [ between both], fits 'the legal requirement' of 'adoption law involving young children'! A simple formula for determining 'which of the two date of birth references, relate to 'the identity of the real biological birth mother', and 'which one is playing the role' of the 'legal birth mother', [within the legal system in operation] involves (a) the 'earliest recorded date of birth' recorded in 'the certificate', between both conflicting dates, and (b) that there is around a three month gap between the latest recorded date of birth, and the earliest..
I am afraid that 'Christine Jay' is or 'was not' the 'natural biological birth mother', of or, to 'Sheila Caffell'. 'She' [in fact] was 'only playing the role' of her 'legal birth mother'.
BUT...
'Diane Moughton' was 'Sheilas' natural 'biological birth mother', as sure as 'night follows day', and 'day proceeds the night'!
I do not think I could in some way, be 'mistaken'!
'Somebody', or 'anybody' (for that matter) who may be 'remotely interested' in 'establishing the stone cold truth', of this matter - [please] try and obtain 'a true copy of the child's birth certificate' which 'confirms' that 'Diane Moughton' gave birth to, and 'put her child up for adoption'. Simply, try and get 'That' birth certificate' from records!
'Good luck' to anyone taking me up on this exercise..