iPhone Storage : App Last Used times wrong ?

Hello

Under the Settings -> General -> iPhone Storage menu, there's a breakdown of how much data each installed application is using, along with a "Last Used" field. If this is supposed to represent the last time that the Application had been used, then it's very wrong. For example is shows one app as not having been used at all, when I know I used it a few days ago, also... its showing an entry for iOS12.1 with the Last Used date of Yesterday.... yet, I have not used it at all, and indeed it's only just been flagged as available for installation.

What is the Last Used field supposed to represent ? Or is is already known that the Last Used Date field is unreliable ?