Thank you GDElla for posting the photo of Alix wearing the Cartier resille necklace. As you can see, it is the necklace that May is wearing in the photo that I posted earlier and is the necklace that Alix wears in the portrait by Flaemeng.
Eddieboy, May may have altered it for her own use. In the photo of Alix it does look higher and longer but the design is quite clearly the same.
As for the photo in the Nadelhoffer Cartier book, I think that this is where the confusion arises and is repeated in Menkes' book. The collier resille in the Cartier book attributed to Alix is not the one that was made for her and must be the source of the mistake. If memory serves me correctly, Alix's collier is illustrated also, either on the same page or opposite but is misidentified......
As for jewellery that has been broken up and re-used, there is a long tradition in the RF of this happening. QV, as we know, recycled old pieces for her own use; Alix reset the Oriental circlet with rubies to suit her own taste; May created new pieces and altered her own jewellery as taste and fashions changed and thw present Queen has followed in this tradition. Her modern ruby and diamond tiara was created in part from other jewels.
The collier resille is very much a fin de siecle piece and would have been out of fashion by the twenties (even though May continued to wear chokers and other such outmoded jewels for years). The choker itself made a bit of a come back in the 1970's onwards; thus we have seen Pcss Anne, Pcss Diana and other royals wearing historic pieces (such as MF's pearl sapphire and diamond choker and May's Cambridge emerald choker) plus their own modern pieces in this style. I suspect that either the collier resillie is too big for anyone to carry off successfully or it has been broken up; if anyone had had the style and guts to wear it, I imagine that Diana would have been the obvious candidate (and to the best of my knowledge she never did so.....)