I just noticed the same thing. The gates are still incorrect
Are you using the FSDT version or the Marketplace version? The marketplace version is still 1.4.2, we didn't want to contribute to clobbering the Marketplace more than already is, with such an inconsequential update, considering we'll have major ones upcoming anyway.
If you use version 1.4.3, the gates in the scenery are correct, which means all M gates DO have the SWA airline code added.
Now, whether the AI you are using respects (or not) those, it's a completely different matter that doesn't have anything to do with the scenery. The only thing we can do to "control" airline assignments is...adding airline codes to the parking spots. SWA WAS in fact missing from M before, now it's there.