Keep in mind that this is a guide from a Lisp using company (bought by Google) who wrote specifically two large applications partly, but significantly, in Lisp: a search engine for flight travel and an airline reservation system. Other application teams may have different rules&requirements, given that they may use Lisp in very different ways.
I'm sorry, my question was based on a four day old memory from the main thread that doesn't reflect what the guide says. It just says don't intern symbols at runtime. Presumably you can pass some kind of a flag to the reader to read lisp data structures without interning the symbols that it reads?
I know the story of ITA well, it and PG's writings are what got me interested in lisp in the first place. Which makes me feel old. But not comp.lang.lisp old, it's all relative!