Most properties that are deprecated don't have a since attribute. We should revisit them and add the attribute so that new entries have it too. Perhaps we should create a rule to make sure it's added?
Comment From: scottfrederick
I have some changes with an architecture rule that enforces the since attribute on usages of @DeprecatedConfigurationProperty in Boot itself, and adding the attribute to the few places that didn't already have it.
The vast majority of the config property deprecations that don't have since are in additional-spring-configuration-metadata.json files. Do you want to add the attribute on all of those also? It will take some time to research the right version for each of them, but I'm happy to do it if that's what you're thinking.