747 freighter main deck numbering

[OneTwoTree]

Good day all.

Quick question. Was watching a CBT about the weight and balance of the 747F and it mentioned
that the main deck is labeled from A-T starting from the nose as “A”, and to the tail as “T”.

It then mentioned that letter “I”, “N”, and “O” are not used.

I checked my weight and balance manual and its correct.

Curiosity is getting to me.
Why isn’t I, N and O used to label the main deck?

[STBYRUD]

I'd guess I and O are omitted to avoid confusion with 1 and 0, but I can't think of a good reason for omitting 'N'...