jix

OK this looks new and interesting, so AC is likely working with Google to sync pricing and match the restriction on AC's promo codes in some markets/directions.

It's set up as some exclusive commercial fare so it doesn't show up in Google or AC's site upon fare review as a promotion being applied, but basically it's still a promo code which shows up in AC email after ticketing

This week's public Halloween code is M984UAP1, whereas the Google flight commercial code is N68XA4B1 after looking at the deeplink and upon ticketing

Using AC.com and/or matrix with &AUTHORIZATION_ID=, both yield the same exact price for a simple one way fare as well as black out days for my sample one way fare.

Can't say if this is good or bad, I suppose it's good for visiblity that one just need to search on Google and see all fares consistently without having to look for a code, but when it comes to changes (AC's promo code rule applies when making changes) I'm not sure how that would work since the commercial code rule is not displayed until after ticketing

Basically to answer the question, since AC system only allows one promo code and Google flight already has it set up, you can't apply another discount from Google flight even though it looks like there's no promo applied.