Hey William -
Apologies for the confusion, but when bulk editing the updates you perform will actually be applied to all the listings you selected on the main listings page, unless you intentionally deselect them.
For example, if you have 500 listings and click "All" on the main listings page followed by the "Edit Listings" button, then all 500 of these listings will be brought into the bulk edit page and selected by default.
In order to control the amount of data that has to be held in the browser and in turn keep things fast, we display 25 listings on screen at a time. However, if you were to for example add a tag, "On Sale", then that tag would be added to all 500 listings (even the ones you cannot directly see). You can scroll and click to see more listings in order to confirm this, but rest assured that upon clicking "Apply" and "Sync Updates" all selected listings will be updated.
Hopefully, this provides a little clarity, but please let me know if you have any questions, or if I can help in any way.
Thanks,
Justin