The aim is to know in which version this feature/bug introduced.
Hi, it sounds like you want a custom field for Maniphest tasks. You can configure a custom field for multiple applications by default using Phorge's configuration, you can also extend Phorge using an extension for more advanced behavior. Here is the documentation on this: https://we.phorge.it/book/phorge/article/custom_fields/
Yes, you could also use milestones and tag the task with that milestone. For example, this is done at Wikimedia's Phabricator: https://phabricator.wikimedia.org/project/subprojects/5539/, where milestones are used to track changes associated with a task.