To answer your question...basically the baggage rules that apply are based upon the fare calculation that is on the ticket.
Scenario 1: Passenger has two tickets: one domestic, one international. Such as, tkt 1: TUS HP LAX 70.00 TTL 70.00 and tkt 2: LAX QF SYD 1200.00YO2 TTL 1200.00USD
In this case, is we check the bags to SYD, HP's rules apply to LAX AND QF's apply to SYD. Let's say $50.00 for HP and 100.00 for QF..total 150.00
Scenario 2: One ticket with the fare being a through fare. That is, a published, single fare using more than one carrier. Such as: TUS HP LAX QF SYD 1200.00YO2 TTL 1200.00USD. In this case, ONE bag rule applies and it is the rule of the carrier publishing the fare; often the over-the-water carrier. This fare would be a Qantas fare in which we are a participant. Some such fares are mileage based, allowing any carrier to the gateway city (LAX) then Qantas to SYD. Sometimes such fares are routing based, the tariff specifies the carriers allowed to fly the TUSLAX portion. But so long as we (HP/US) are part of the fare's calculation, this is all we need to know as to which rules to apply. Then we must look up or call QF or rates to determine the amount to charge.
Even US publishes international fares to cities we don't fly to. We may sell a fare from PHX to MOW (Moscow), for example, using US from PHX to FRA, then SV to MOW. Such a fare is a through fare, one baggage rule, the US rule, applies to Moscow.
All this is something many East agents don't know. However, with East agents, it seems nobody knows this stuff. It's not to be found in the computer, in training, no place at all! Tempe is the environment in which the airline operates yet Tempe hasn't a clue about such issues. This is also an example of many other topics they've never dealt with. How can we handle such things they don't know even exist?
Our flights to Europe have passengers with destinations beyond FRA, MAD, etc. When we must rebook them, how can we do so with a computer that shows no schedules for thousands of city pairs around the world? Not only is Shares tedious to use, but it simply doesn't have things we need to do our job. I can't tell a passenger from a cancelled flight that I can't rebook them or reticket because our computer hasn't the availability displays I need.
This is going to be scary!