Periodically, I enter a handful of special search terms into B-Seek looking for clues on upcoming or unannounced releases. If the search yields results, the UPC and SKU automatically come back in the search results. I did just now test the one of the SKUs by going to W-Mart . com, finding any Lego listing and going to the product page, then replaced the SKU at the end of the URL with one of the ones in the screenshot I posted (even if parts of the URL still reference a different set). Press Enter and it refreshes the page and does pull up what looks like a legitimate placeholder listing with no picture and "This item is no longer available" (which really means this item is not yet available). I think as part of the sales and inventory planning process Wal-Mart must prepare their databases in advance. Before technology like B-Seek, Wal-Mart's process kept the new listings rather hidden. Now days with the new tools, the old process is inadvertently revealing clues to those interested enough to search for them.
Search terms I use every couple months searching Wal-Mart via B-Seek . com:
Lego 2018, Lego 2019, Lego IP, Lego conf, Lego confidential...