2.2.5 [W3C-XSD] Section 3.2.14, gMonth
The specification states:
Since the lexical representation allows an optional time zone indicator, gMonth values are partially ordered because it may not be possible to unequivocally determine the order of two values one of which has a time zone and the other does not. If gMonth values are considered as periods of time, the order relation on gMonth is the order relation on their starting instants. This is discussed in Order relation on dateTime (§22.214.171.124). See also Adding durations to dateTimes (§E). Pairs of gMonth values with or without time zone indicators are totally ordered.
Indeterminate comparisons are considered to be determinate.