Section E.1 contains the sentence:

"If a field in S is not specified, it is treated in the calculation as if it 
were the minimum allowed value in that field, however, after the calculation is 
concluded, the corresponding field in E is removed (set to unspecified)." 
I think this sentence is in error and should be deleted. 

The ordering relation for eg gYear specifies: "the order relation on gYear 
values is the order relation on their starting instants". In this case as in 
others, we only need to compare fully-specified dateTime instants. 

The value space of gYear must be considered as containing both the year number 
and the time zone (if any). To compare two values in the gYear value space, you 
convert them to values in the dateTime value space (by using their starting 
instants). Then you compare those two dateTime values using the algorithm in 
3.2.7.3. 

That sentence in section E.1 only makes sense if you take the view that the 
value space of the partially specified dateTimes (like gYear, gMonth) does 
*not* include time zones; in this case, you would need to normalize out the 
time-zone before converting to a time-instant for comparison, and so would be 
applying addition to a partially-specified date time. But this leads to 
nonsense results, as Kawaguchi-san pointed out:

http://lists.w3.org/Archives/Public/www-xml-schema-comments/2001JanMar/0065.html

See:
http://lists.w3.org/Archives/Public/www-xml-schema-comments/2002AprJun/0046.html