Hello Lang,

Lets see if we can help you on this question.

You are correct in your obervations that you can have many diiferent seating codes for the same cabin class. These are down to the cost of the ticket and the flezbility that you get with dates and refunds. Below are some examples.

First Class:

F- Full fare, fully flexable and transferabel between airlines on the same route.
A- Discounted first class, fully flex but only on BA

Biz class:

J- Full fare, flex, refund, multi airlines
D- Felx, refundable before departure?
I- Cheap(ish) non flexi or redundable

Economy:

Y- Full fare, flexl refund, mutli airlines
M,K and others cheaper with restrictions.

I am sure ScottC or somebosy else with vast knowledge will add to this or correct me soon.....