While Google Product Listing Ads traffic for most advertisers is comprised almost entirely of non-brand search queries, there are some sites, particularly manufacturers, that see a large amount of PLA traffic coming in through queries that include the advertiser's brand name.
This can skew reporting accuracy if PLAs are designated as a fully non-brand endeavor, as well as hurt the accuracy of bids if the branded queries are making target performance look better than it should from a non-brand perspective.
To identify if your PLAs are showing for branded search queries, check search term reports regularly for branded searches. If the percentage of traffic that is branded is high enough, you may want to try to segment this traffic in some way.
One option is to launch a duplicate All Products target, and apply brand negatives to the original set of targets, as well as add negatives for head non-brand queries to the newly launched brand target.
PLA advertisers will need to add negatives regularly to the brand target in order to narrow the scope of traffic going to this target to just brand queries as best as possible. The bid for the brand All Products target should also be kept lower than the bid for the non-brand All Products target in order to keep as much non-brand traffic going to the correct target as possible.
This solution not only helps to ensure transparency in reporting on brand vs non-brand, but also allows for more accurate target bids on non-brand searches.
It might not always make sense to add an additional target, especially if branded queries make up a tiny amount of traffic going to your PLAs, but it's still important to understand how much of your PLA performance is coming from branded queries as Google continues to broaden the types of queries that return PLA results.