So I have archive.php which uses a sidebar (fishyPG_sidebar) and blog.php which is a copy of archive.php.
In my functions.php there’s only one sidebar registered.
I was thinking the results would be that fishyPG_sidebar would be displayed on all the pages that use either one of those templates. Instead:
Pages using blog.php display some weird sidebar I didn’t make (and doesn’t display posts but I haven’t even looked into that yet.) and pages that use archive.php display no sidebar at all.