Hello Greg, I think I got it.
When you say that Intel "retires some part number", you probably mean that Intel has stopped to talk about some architectures (or cpu families) in its official documentation. And "working entry" should mean that those cpu-families are still valid, at least conceptually, today. Furthermore, today's "part numbers"/architectures/cpu-families on Intel manuals are them of the QUARK family.
Finally, as for the book you suggested (Computer organization: hardware/software by Gorsline), the point is simply the fact that it talks about those "part numbers"/architectures/cpu-families that are not anymore on official Intel's documentation.
Cheers