@WantItToWork, coincidentally I just went through this testing after becoming frustrated at the Photo Streams Screensaver omitting pics from a slideshow I was building.
The 'gist is that the Photo Streams Screensaver (distinct from its Slideshow) will only pull images from the 20 most recently enabled streams, with a max of 5 streams selected randomly from among the 20. Further, the image selection depth (how far image selection will dive beyond the last image within a given stream) is 100 for a single enabled stream, and (200 / # of selected streams) otherwise.
Probably simplest to illustrate...
(Random stream selection also demo'd in this Google Sheets spreadsheet.)
Changes/fixes needed include...
- Randomly selecting just 5 active streams is probably OK, but no reason to limit the scope to just the 20 most recently enabled streams.
- Per stream image selection depth would ideally be eliminated, allowing random selection from the entire range of available images for each stream.
- Limiting a slideshow instance to just 100 (or some other limit>= 100) is probably OK, if it's a resource issue, but an alternative fix would be to allow a configuration option to trigger the Photo Streams Screensaver to reinitialize after a set number of slideshow passes complete, avoiding a single set of 100 slides cycling endlessly.
p.s. Google Photos albums and Sheets spreadsheet used for the testing are available, if needed.
A bit more of the same, detailing the image selection depth limitations in table form ... plus tabulating the "orphaned" image count were each stream filled to capacity w/ 1000 images.
