I am not asserting that the State failed to turn over the letters in a timely manner.
However, to answer your question, let's assume that the State had failed to turn over the letters in a timely manner. Casey may have written the letters (more about that in a moment) but there is no evidence that she had a duplicate copy of them. Thus Casey could not provide a copy of those letters to Baez. Certainly Baez is entitled to know the content of the letters, in order to meaningfully "confront" this evidence against his client.
Additionally, sometimes jail/prison inmates are not the most honest and trustworthy of people. It is not impossible that an inmate might claim to have letters or other communications from Casey, but the letters turn out to be forgeries and/or the communications turn out not to have occurred. Again, Baez is entitled to an independent inspection and evaluation of the letters' authenticity to meaningfully "confront" this evidence against his client. If the letters turned out to be forgeries then their content would be completely irrelevant and the letters would be inadmissible.
Thus, assuming the State had failed to turn over the letters in a timely manner, Casey's rights (as well as the statutory reciprocal discovery rules) would have been violated and her defense would have been prejudiced.
Katprint
Always only my own opinions
Baez's motion re: delayed turn-over of discovery talked about the letters TO Casey, not the letters from Casey. (Letters from her adoring fans, Cindy, and George, to name a few.)