Notification threading not working as desired / expected?

We have some long running chat threads that started months ago and are still receiving updates, each time there is a notification with an identifier matching the original notification. For example:

My understanding based on the [`threadKey` test cases](https://github.com/guardian/google-chat-utils/blob/b8419ed49c604fc860787d25a9e88c4cabb0371e/tests/gChatUtils.test.ts#L314) is that notifications / updates _should_ appear in their own thread if they have a matching identifier but a different date. In practice, this doesn't seem to be the case.