Since at least 1927 Gibbons have had the issue date of SG207 as August 1871.
Basset Hull, Hutson & Lowe all state April 1871.
I picked this up while doing my research and advised SG and they rightfully asked for evidence of an example dated between April and August.
Then this pair turned up.
You can clearly see the W of the watermark on the left (as you're looking at it in the photo) stamp.
I'm in the process of writing a monologue on the NSW DLR stamps and will post it here (but not all at once!) when done.
Thanks again folks