Upon reading through some of the sections in this book, you may notice that a lot of the packages linked in some of the sections aren't in this book but rather in BLFS, some optional dependencies aren't listed, some packages may be outdated, and some packages that have test suites don't have test instructions. These choices are very much deliberate.
Many packages linked on some of the packages' sections aren't in the book but rather in the BLFS book. There are multiple reasons for this, but the most notable one is the packages that aren't in the book aren't important for the main packages in the book, those being Steam and Wine. They are still listed anyway if users want more support out of the specific packages not specific to the main packages, like media playback for example. Another reason for packages not being in the book is that the packages take a lot of work to install and require jumping around. They can also require a lot of choice or take up space or RAM for no real benefit for a lot of users when there are more simple solutions.
There are some optional dependencies that aren't listed, and the main reason for this is that they just would take up unnecessary space. If on the offchance you desire even more out of your system, there are plenty more packages in BLFS and BLFS is more geared for everyone, although this book focuses more on gaming. Usually the optional dependencies that are not listed are those that are needed for testing builds and generating documentation.
No packages are currently outdated at time of release.
Many packages have test suites which can test a given build for any potential bugs and may tell you if something has gone wrong. However, in GLFS, a lot of these packages have test suites that depend on packages that aren't necessary in the book and would make this book larger than it needs to be. Furthermore, a lot of the packages that do have test suites aren't involved with critical components of the system and don't tend to have bugs that come up as a result of a build, but rather the released source code itself. If you want to do test suites of a given package, BLFS has good instructions for that on each package and covers all the required dependencies, as well as instructions on how to install those dependencies.