She only read its description from Verin's list of the known ter'angreal stolen by Liandrin. Neither Egwene let alone Mat ever came close to those dices (it needs channeling btw, it's useless to Mat).

Basically, it's like RJ wanted to plant a red herring that some ter'angreal can warp odds and that one like this was stolen by the Shadow, in the book where Mat's luck starts to become a focus, to make the readers wonder for a while what's up with Mat - if it's Lanfear manipulating him etc. Mat's luck is natural, just massively multiplied by the fact he's ta'veren. That became clearer in later books. With Mat it's just extremely obvious because nearly everything he does in life is to him like playing the odds or gambling... But we know this is a characteristic of ta'veren. Hawkwing was quite lucky, and the Forsaken described LTT as extremely lucky.

Btw, the last we ever heard of this ter'angreal in the series was in TDR 25, outside the range of chapters mentionned by Brandon.

One of the "loaded gun" in those chapters is the final revelation of his imbroglios with the Red Ajah re: his nephew (and ask yourself why he truly went to TV at the time of TDR...). Moiraine promised to tell him the names of the Red sisters involved when they saw each other next. They are together now. It did not really start there, but from BS's perspective and depending what happens, he might associate this in his mind with those scenes between Mat and Thom in TV.

Not that's the only possibility of loaded guns in those chapters... there are several options.