Wonder if those gizmos you see when you walk in the grocery that let you scan items as you shop would lock in the current price.
Good question. When I worked in a grocery store, outsider the weekly sales, any mid-week changes generated a increase/decrease price report.
Some price maintenance clerks wold print it, stuff it in the dept. mail box, which was normally cheeked once a day around 8 - 10 AM, and just apply the changes which usually came down around noon. Only reason you would know was when the cashier supervisor called and asked to verify. The smart ones would print new signs, walk the store and deliver them all to the depts and you knew by the time they got back to the office, they would apply the changes.
I see the digital sings eliminating the issue of old signs.