Hi B17_fan,
I have the transcripts for Mildenhall from the WiltsFHS.
I don't see a baptism in 1768 with a note "BT Greenaway"
However, in 1769 there is a baptism for Mary Greenway 16-7-1769 d/o John & Sarah with the note (BT Grenaway). I'm sure you will find it means Bishops Transcripts record the name as "Grenaway" whereas the parish register says Greenway. Just a mis-transcribing when the BTs were written.
Is this person you refer to?
Alan