Those locations probably had t nuts from the underside originally, which are common to have locktite on system 11 games. People will snap the screws if not careful removing them, and this was probably someone's fox. Look at the wood surrounding those holes under the playfield and you'll probably see 3 marks from where the spikes of the t nut used to be.

Edit: I've restored numerous system 11 games but never had an ES, so I'm not familiar with those particular posts or fasteners and could be wrong about them being t nuts. Actual mileage may vary depending on driving habits, contents may settle during shipment, sold by weight not volume, some assembly required.....