✔ 最佳答案
These are called the sub-class, they represent the different ticket condition and regulation with the Economy Class...
Usually, these different sub-class would have different condition and regulation... And as the ticket is cheaper, the more condition and restriction there would be like you said limiting the flight you are allow to take (eg. early bird flight), restriction on maximum staying time, date of flying (eg. Monday-Thursday flight only), non-refundable, no change of date etc...
But if your ticket is more expensive, usually it would allow you to fly when you want on the route with more or less no condition and restrictions apart from maximum staying time being 1year and allow to fly when you wish if there is seat available on that flight...
For those not allow to fly on flight 9051-9100/9401-9450/9601-9700... Its usually because these are code-share or charter flights... For code-share, usually you would need a higher sub-class ticket (more expensive ones) to fly on them and if its charter flights, then that means these flights can only be booked via travel agency as its being chartered by them...
