You can only use SWUs on flights that are both operated and marketed by AA, so trying to use one on a partner flight won't work. You can use an SWU on the AA flight on 2/1 if you have SWUs that were awarded in 2018 as they expire 1/31/20. If you have one that expires 1/31/19 and you also have ones that expire 1/31/20 then you can use the expiring one for the 2/1 flight if there is immediately confirmable space, by calling and saying you want to use an SWU on the flight and don't say anything about which SWU or flight dates. Let the agent do the usual processing; the system first checks that you have valid SWUs (expiring 1/31/20) and then will pull the oldest one anyway.