I have explained it a few times now. But I will again for clarity.
Jobs are scheduled (if there are changes in the last 24 hours and an image will be built, it does not check it an image of that hash exists already.)
Jobs are also run manually, in this case the RPi ones were run to address a RPi 2GB built “quickly.”
There is nothing to be read into the images with different dates and the same hash. There maybe many of the same hash, you are welcome to use any off them, though the contents will have different compile dates, they will be from the same source.
Hope this fully answers the questions.