Couples with multiple stages

[Aldemarprins4]

Hello friends, I have a problem with some transactions, and it has to have a start stage (1. Process) and two output stages, a main output stage (2 Distribution) and the other alternate (3 Distribution), the Alternative stage should only be used when the main stage is null, that is, it is not found in the file.

The pairs should be as follows:

Arrival Stage Departure
02/11/2021 13:31:27 1. Process 02/11/2021 14:11:38
02/11/2021 14:12:02 1. Process 02/11/2021 14:12:03
02/11/2021 14:18:27 2 Distribucion 02/11/2021 14:18:28

02/11/2021 14:50:42 1. Process 02/11/2021 15:03:51
02/11/2021 15:10:41 3 Distribucion 02/11/2021 15:10:42

02/11/2021 16:31:27 1. Process 02/11/2021 16:11:38
02/11/2021 17:12:02 1. Process 02/11/2021 17:12:03
02/11/2021 18:18:27 2 Distribucion 02/11/2021 18:18:28

All the information is in a single file and is organized by the order of arrival

[Aldemarprins4]

I have this code but it only takes one stage, that is, the main one, when I put the second stage it does not work for me because the other stage appears

alt(Peek(Pareja),1)-(Stage ='1. Process' and Previous(Stage )=2 Distribucion) as Pareja

I don't know if you understand me or if you require any additional information