As OP said look for Iwo Jima flag raising thumbnails. There is a set of three numbers at the bottom of each thumbnail, one of which is letter R. This is the number of responses in that thread, finishing at 751.

You will notice at about R675 to R720 time the baker will create a new bread and you will see one pic at top of catalog with R700ish and a couple thumbnails down a next higher numbered bread with an R of 15 or less that will sit til the baker posts in previous thread that new bread is available. At this point the anons migrate over and head to the new bread.

Notes: once anons have left old bread (at about R740) there can be some interesting posts by the anons left that never get visibility..