If you already have Amy and John's marriage certificate, then I doubt that the parish register entry will show any additional information.
If ordering the birth certificate for the unnamed female in 1902, you can use the father's name as a reference checking device. If it turns out that the baby girl had a different father, then it will only cost you £3.00 (instead of £7.00 for a - possibly - incorrect certificate).
Presuming that the certificate is the correct one, it would also give mother's maiden name and from there we could have a look for a marriage for them!
Pennie