Thank you. Over the evening I also ran across TR3446 which clarifies it on page 10, table 1.
SnapMirror volume replication is block-for-block replication; it transfers the file system verbatim.
Therefore earlier major releases of Data ONTAP cannot understand file system transfers from a later
major release. Data ONTAP 7.2 and 7.3 and 8.0 are examples of three different major release versions.
Data ONTAP 7.3.3 and 7.3.5 are examples of same major release but different minor releases. Table 1
shows version restrictions for volume SnapMirror.
Table 1) Volume SnapMirror version restrictions.
Volume SnapMirror Source Volume SnapMirror Destination Replication Possible?
Data ONTAP 7.2 Data ONTAP 7.3 Yes
Data ONTAP 7.3 Data ONTAP 7.2 No
Data ONTAP 7.3.x Data ONTAP 7.3.y Yes
Data ONTAP 8.0.x Data ONTAP 8.0.y Yes