The XDM Recommondation defines primitive simple types as ``There are 23 primitive simple types: the 19 defined in Section 3.2 Primitive datatypes of [Schema Part 2] and xs:untyped, xs:untypedAtomic, xs:anyAtomicType, xs:dayTimeDuration, and xs:yearMonthDuration], defined in 2.6 Types.'' xs:untyped, however, should not be an atomic type. (Also note the calculation error: 19 + 5 = 23?)
You are quite right - xs:untyped needs to be removed from the definition in 2.1 and the entry in the glossary in Appendix D