The Fixed Layout properties section of the RS spec makes a number of informative default statements for the various rendition properties, but only one of them is a normative statement.

The default value reflowable MUST be assumed by EPUB Reading Systems as the global value if no meta element carrying this property occurs in the metadata section section [EPUB-33].

The default value statements for rendition:orientation and rendition:spread are both informative (and the same).

The default global value is auto if no meta element carrying this property occurs in the metadata section.

I would propose making these both normative MUST statements to match the statement made for rendition:layout and to clarify this section.