I'm curious about how eTicket numbers work as it seems to be always discussed rather vaguely.

I've sometimes had itineraries composed of multiple consecutive eticket numbers. What causes this to happen? Is it a straight-up "different fare components have different eticket numbers" rule? What I've found confusing in the past is that return-trips seem to all have the same eticket number, which leads me to guess that it's the fare component that matters.

One of my booked itineraries currently (rather strangely) shows the eticket number of flights earlier on in the itinerary as "after" the eticket number of flights later on in the itinerary. In other words, the eticket number of the first set of flights are "n+1" whereas the eticket number of the last set of flights are "n". Would this pose any problems? Is there a distinction between eticket numbers and "coupons"? (I recall frequently reading on fare rules "coupons must be used in order" or words to that effect). There was a schedule change on the itinerary, if that's relevant, though I can't remember if the ticket numbers switched when the schedule change happened or if they were always that way.

Hoping someone with a deeper understanding of etickets can shed some light.

So all of this terminology goes back to the days of paper tickets. Others that remember better will probably correct me.

Each paper ticket had a bunch of coupons. Each coupon would be a leg. Each paper ticket could have a maximum of "n" coupons, and if you needed more than that you'd have to have multiple tickets with different ticket numbers issued.

"coupons must be used in order" means that you have to fly the segments in the order ticketed, or in other words - ticket book coupons must be torn off in the order that they're written.

In the era of e-tickets, there may still a limit to the number of segments/coupons you can have (primarily due to the antiquated systems that GDSes use), so that may require multiple eticket numbers, although I don't think I've seen this lately.

Any time your e-ticket has to be reissued, a new number gets assigned to it, but the PNR history still contains the old ticket number.

I'm guessing you know that a PNR is now like a ticket booklet, containing all the relevant info about the segments, their order, etc., as well as the ticket number. If multiple airlines are involved you may have multiple PNRs, one for each airline, and possibly one for the GDS.

Each ticket # still has a maximum of 4 coupons, and I believe that no more than 4 ticket #s (i.e., 16 segments) can be issued on one PNR.

Thanks for your help. So, is it possible that the schedule change in my itinerary caused a new set of eticket numbers to be issued, and the OTA page is still displaying the old ones "jumbled up"? And would you say I should be concerned at all about my eticket numbers getting "jumbled up"? Would it cause any conflicts with the "coupons must be used in order" rule, or is the concept of eticket number distinct from that of a coupon?

Yes it's possible. If you're ok with the schedule change, you can do nothing, or you can always call the OTA and ask them to make sure your record is synchronized. Worst case scenario, if something's not synchronized, it'll get synchronized at check-in. If you don't like the schedule change, then you need to call.

Ah, this brings back memories of the old red carbon copy 7+part ticket forms that we all used to have to carry around... and which had to be sent back to the airline offices for accounting which must've been such a PITA. Do any of those still exist?

I see. So it's possible there's an entirely new set of eticket numbers sitting somewhere with the updated itinerary, and the OTA page doesn't show it yet.

Do you know of any online service that I could use to find this new eticket number?

The airline's website - the one that issued the e-tickets.

Depends on the airline but you can try CheckMyTrip.com with the PNR and surname and see if it pulls up the details.

Also, generally speaking there is minimal value in a passenger knowing that number. Is there something in particular you're looking for?

The quickest way is to just call and ask the carrier that created the record to just read them to you. You could also get them from the airlines refund site if they have one. For instance, for American, it's refunds.aa.com.

I'm also assuming you're only talking about carriers that follow established IATA procedures for tickets. Some, like Southwest and Jetblue, don't.