I found an interesting behavior today: I accidently named a data upgrade script
data-upgrade-0.1.20-0.1.20.php where it should have been
data-upgrade-0.1.19-0.1.20.php, and it actually has been applied.
And as I cannot find a question here that can be used as a reference for the setup script version logic (correct me if I'm wrong), let's use this one.
By which logic does Magento execute the install and upgrade scripts?
Especially interesting edge case: When and why are scripts like
upgrade-1.0.0-1.0.0.php executed, where the "from" version number is equal to the "to" version number?