I thought I knew the rules for open tickets...
 

Tried to book a AONE4 ex-CAI for next year with a confirmed date for BA's CAI-LHR flight and all other segments open. The AA RTW agent said that I needed to have a confirmed date for the first intercontential flight as well. I don't think that is true for areas 2 and 3. Who is correct, me or AA? I suppose I could have given any old date and changed it later.

FWIW, my ex-CAI AONE5 purchased from AA has only CAI-LHR dated, all the rest open.

The relevant rule is clear:

87N RESERVATIONS FOR THE FIRST INTERNATIONAL FLIGHT, AND
88N ALL PRECEDING FLIGHTS, ARE REQUIRED AS FOLLOWS:
89N .
90N ------------------------------------------------------
91N I ORIGIN IN AREA 1 I ORIGIN IN AREA 2/3
92N ------------------------------------------------------
93N I 7 DAYS I ANYTIME PRIOR TO I
94N I I DEPARTURE OF THE FIRST I
95N I I FLIGHT. I
96N ------------------------------------------------------
97N . * ALL OTHER FLIGHTS MAY BE OPEN.

But one complicating factor is:
2N SEASON
3N ------
...
10N . * ECONOMY CLASS - DETERMINED BY THE COUNTRY OF
11N . TICKET ORIGIN.
12N THE DATE OF THE FIRST INTERCONTINENTAL FLIGHT
13N DETERMINES THE APPLICABLE SEASONAL FARE FROM THE
14N COUNTRY OF ORIGIN FOR THE ENTIRE JOURNEY.

So in Business or First it really doesn't make a difference, but if you are travelling in Economy then I can see that there is in fact a conflict between line 97 above and the requirement in line 12. I've not noticed this before since I don't do economy long haul, but I can see it might be a problem.

From the * file -
Talk to another rep.

If it's ex-CAI then I don't think the season is a factor (even if you're doing it Economy)

My ticket needed to have the LHR-LAX one dated as well, not only CAI-BCN.

Seperat question: How do I make reservations in a different PNR than the ticket and the dated segments?

To reserve open segments just call the airline you want to fly on and make a reservation. Tell them you have an open "x" class ticket and give them the ticket number for their records. They will create a PNR in their system for you for the flight. If you make multiple bookings with the same airline at the same time, you will only have one PNR, separate bookings (if you don't mention the one made previously) or bookings on different airlines will result in a PNR for each booking.

Thanks. I'll do that then!