Thanks to everyone for all of your responses. All very helpful and appreciated.

I have a question about requesting an upgrade. Adam Smith mentioned you could use your Eups then change to the complimentary once that window opens. As 50k flying Latitude, it seems I can request my Eup upon booking since the window is 'anytime' for that fare class. Then the complimentary upgrade window is 2 days; so would I cancel the regular Eup then and make the complimentary request? Does one have precedence over the other? I'll be using all of the 10 flight credits by the end of 2019 and have enough Eups for about half of those credits so would like to make best use of the 2 upgrade options.

Also, if I can't upgrade, are Preferred Seats complimentary for the Latitude Pass?

Thanks again!