Those are the new Inside Macintosh series, published starting in 1992. SpInside Macintosh, the HyperCard stack from which the web page linked in this item was created, was produced from the first five volumes of the original Inside Macintosh series, published from 1985 to 1991.
As the Preface to Inside Macintosh: Overview (1992) explains:
The original Inside Macintosh library of books appeared in six volumes from
1985 to 1991. Those volumes each focused on a particular version of the
system software, sometimes prompted by the release of new hardware
configurations. Often, the later volumes of the original Inside Macintosh
described only new system software components or changes to existing
system software components.
The new Inside Macintosh books are intended to replace the original Inside
Macintosh books and to provide a more complete and more useful reference to
the Macintosh system software. The most obvious improvement in the new
books is that they are organized principally by topic. For example, the book
Inside Macintosh: Files contains virtually all the available information related to
files, including complete descriptions of the File Manager, the Standard File
Package, the Alias Manager, and the Disk Initialization Manager. Similarly,
the book Inside Macintosh: Text contains all information about handling text.
This topic-oriented organization of books makes it easier for you to find the
information you need. It also makes it easier for Apple to add books to the
Inside Macintosh suite as new technologies emerge in the years ahead.
As the Preface to Inside Macintosh: Overview (1992) explains:
If only they’d kept that up...