I think if they are mentioned, they should be documented.  Removing mention of them would be fine with me.

Looking at this again, I think the description of Py_TPFLAGS_DEFAULT is no longer accurate.  It reads: "This is a bitmask of all the bits that pertain to the existence of certain fields in the type object and its extension structures. Currently, it includes the following bits: Py_TPFLAGS_HAVE_STACKLESS_EXTENSION, Py_TPFLAGS_HAVE_VERSION_TAG."

But neither of those flags pertain to the existence of certain fields, do they?

Perhaps it should simply read: "This bitmask should be set by all types to define certain bits used internally by Python."