See theory #2 in my previous post. Also, CX sometimes swaps a regional plane with J and Y with an intercontinental plane with F, J, and Y. As another poster mentioned, a common numbering system creates less havoc when an aircraft swap occurs. Also, other widebodies of CX have J starting at 11.

Note that CX skips row 4 and 13. 4 is a bad luck number in Chinese culture. Silly, if you ask me regardless of culture, skipping numbers for superstitious reasons.