Putting languages files in the theme are not required. If a theme author chooses to include a POT file in their theme it needs to be kept up to date with all translation strings.
Some of the theme authors directly download the underscores theme and work on it and forget to make their own theme POT file and keep the default underscores POT file. Also, some theme uses their own theme POT file without updating.
Some example text I found in POT file is,
Copyright 2014, # Copyright (C) 2020 Automattic
We can find those strings and the date of the POT file creation "POT-Creation-Date: 2020-04-17T21:03:15+00:00\n" and restrict the upload or give a warning message.
Putting languages files in the theme are not required. If a theme author chooses to include a POT file in their theme it needs to be kept up to date with all translation strings.
Some of the theme authors directly download the underscores theme and work on it and forget to make their own theme POT file and keep the default underscores POT file. Also, some theme uses their own theme POT file without updating.
Some example text I found in POT file is,
Copyright 2014, # Copyright (C) 2020 AutomatticWe can find those strings and the date of the POT file creation
"POT-Creation-Date: 2020-04-17T21:03:15+00:00\n"and restrict the upload or give a warning message.