I just did a response, but it has disappeared.
Thank you to Propero for explaing Ninas. Unfortunately, I don't have enough answers to find any. I have still to get any in the south west corner and am short of a few in the south east. I was pleased I got 7d and 9ac, but can't see their significance.
Please can I have some hints: for 21 ac. Is the definition development? 20d I've no idea. 28ac I'm guessing it starts REP.