You might remember a decade ago when everyone wanted a digital photo frame, but those devices were all junk. In the era of smart displays, we finally have good digital photo frames powered by Google Photos that happen to do a lot of other things, too. The experience is getting a bit better today with the addition of dates in the photo slideshow. However, they only appear on some photos.
When you set up a smart display, Google lets you choose if you want the ambient display to show a generic art gallery, a digital clock, or your own photos. If you choose your own photos, you can let Google randomly use recent highlights or pull from a specific album. Before today, every photo included the owner/uploader and album name in the lower right corner. Now, some of the photos have the date and number of years ago they were taken.
So far, it looks like very few photos show a date in the slideshow, Artem reports it's around 10-20% for him. We're not sure why only some photos have this. It might just be the older that show the date, or it could be completely random. Google may also be testing this feature, and it'll work more reliably later. We've only verified this is happening on Google/Nest displays, so it could be exclusive. It's hard to say what Google's up to with features like this.