Good spotting Beth, the choker/ bracelet is an impressive piece as are all of QM's jewels. I wonder if their is not an app where we could put black and white pictures in colour as I am aware the technology exists and that's the only way I can decipher. Beth in your 04th picture, is QM not wearing the Russian sapphire broach with a pear shaped gem attached? Please look again and see if my observation is correct.
The latest firm dating I have for the brooch section of the chain link bracelets/choker is when Queen Mary wore it for the Silver Jubilee in May 1935.
Details from Silver Jubilee photos
I have two other images but I am not sure of the dates.
This detail is from a Shutterstock image which is said to be Queen Mary at the Silver Jubilee but she is wearing a different hat, has a different hat jewel and slightly different hair arrangement. In the full photo she is seen with the two Cullinans as a brooch which she did not wear to the Jubilee service.
The photo I initially posted was from the Trooping of the Colour in early June 1935.
I wondered if somehow the outer sections of the brooch could be removed (or even air brushed out of the photo) but when I put a photo of the brooch as it exists today against the 1935 Trooping of the Colour photo, the shapes do not match in my opinion.
The Trooping of the Colour photo might have been extensively retouched for publication and so is giving a distorted impression, but I don't have enough knowledge or experience to gauge that.
If 1934 brooch hasn't been seen since 1936 then it could have been altered for the choker. It does look like it could contain a diamond of around 9 carats in the centre.