XS186 was indeed a later production T4 than XP688 along with several others in the T4 line.
She continues to make good progress towards a frustratingly limiting taxiable condition, after almost giving up altogether and becoming part of the undergrowth in Suffolk a few years ago !
If any of you have XS186 in your flight logs (1964-68 at CAW Manby) please let me know, i have Pat Cunningham and Peter Cowen (ex Macaws) who have found flights recorded so far..........