Hi Bruce,
You may interested in a report Arup released with Saint-Gobain: Carbon footprint of facades significance of glass - Arup
Anecdotally I’ve heard that at least one US float glass supplier can only use cullet generated from their own glass due to a specific chemical in their formulation, so this seems to preclude any post-consumer cullet. Appears to be validated by a lot of these sources citing pre-consumer cullet rates.
Our facade engineering team has also been looking in circularity opportunities - mostly using mechanical vs. chemical connections to facilitate reuse.