MC965LL/A - thats the number of Macbook Air 13 inch.
MC975X/A - that should be number of... 15 inch Macbook Air .
It seems to me that there are part numbers missing then based on the current line up, which has two model numbers for 13" and 15"
MD313B 13" MBP low
MD314B 13" MBP med
MD318B 15" MBP low
MD322B 15" MBP med
MD311B 17" MBP -