My copy of the Matrix cookbook is dated November 15, 2012, and is the newest copy I've been able to find.
Identities may not change overtime, but the approach to an error-free presentation can be asymptotic, and some topics may be missing. Where can I find an up-to-date copy?
The address "matrixcookbook.com" listed in the 2012 book is defunct, the email in the book doesn't work, and the 2302.dk website seems to be out of commission, and I haven't found personal sites for the authors.
I'm making good progress---360 equations---on compiling a matrix mathematics reference Matrix Forensics here. Crucially, the LaTeX source is available so that others can contribute and add to it over time.
The compiled PDF is available here: https://github.com/r-barnes/MatrixForensics/raw/master/matrix_forensics.pdf