Ben - many thanks and sorry no, none of the historic aerials I have seen extend to that part of the course. If you look on the Patric Dickinson course plan Sean reproduced, these abandoned holes were at the far left-hand part of the plan, beyond the current 16th.
The last really big scheme for amendment of the closing loop was that of Hawtree in the mid 1960s, and this fascinating plan is reproduced in my history of the club: the Hawtree scheme would have involved changing the 14th (into a doglegged par 4), a new 15th (downhill short hole from the dunes aimed on the castle), an amended 15th becoming the 16th, existing 16th unchanged as the 17th, and a new 18th (the latter becoming a par five, dog-legging from the existing 17th tee to the 18th green, which would have made a cracking finish). But in the end lack of funds and scepticism amongst senior members of the club and the numerous internationals and Walker Cup players who belonged to RStD in those days rendered the whole still-born. It is a great seaside Might Have Been though, which in 2019 the Club would never be allowed to undertake (as the whole site is now governed by Natural Resources Wales and various scientific rules).