Roy, we've got some questions on how Google tracks and exposes performance data for Google Shopping Campaigns. Could it be possible that performance follows SKUs in Google Shopping when product groups are split or aggregated – but not when they are moved via updating a value in the feed?
We’ve seen that it takes several hours to move between product groups in PLAs when done via updating a value in the data (in this case the custom label 0). We pushed a feed with updated values to merchant center at noon. At 3PM very few items had moved. By 4:30 about 1/2 of them had moved and by 10:30 all items had moved. This had to do with products moving from our store to our outlet, which has a different URL path. It appears to us a move like this doesn’t bring any of the performance data along with the SKU.
This is a great question and I expect it will evolve as Google continues its push with Google Shopping Campaigns in general. Performance data is kept at the product ID level since this is unique to your data i.e. your feed and account. Google stores the data at this level. However, in my experience it doesn't retroactively apply that data to new product groups based on new dimensions.
For example, say you just added a new custom_label for price tiers (a favorite optimization strategy of mine). The day after it's added, if you break out a Product Group by all of the values of this new field, all of the conversions will appear in "Everything Else". When you click to examine the products in that "Everything Else" bucket, it could be entirely empty, and the conversions are still there. However, if you broke it out by product_id at the top level (which none of us could literally do, as it's limited to 1000 leaves per branch, and most of the sites I work on have catalogs bigger than that), then you would absolutely see the product conversions at the level described.
However, if you refactor a taxonomy after a couple of weeks, conversions since that change are totally portable from one place to another. If you already have "store" and "outlet" branches, it may transport them cleanly. If "store" and "outlet" were totally new, then I think you'd have to do some kind of performance aggregation through AdWords Scripts or API reporting, since the ProductIDs would still have data, but the new Product Groups wouldn't. That may change in the future, as making the product_id performance totally portable would be really cool, and not technically difficult for Google to switch.
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