Does moving content update any date field?

Hi there, I'm looking to use the API to get a list of root messages from the platform (depth=0). However there are a lot of messages (nearly 3m) so getting a full inventory every time is impractical; what I'm looking to do is get an initial full list and then update that list with a delta of messages that have been either created since the last pull or edited somehow. The field that I've been using to pull the delta is conversation.last_posting_activity_time. However, it now appears that I've got a bunch of content showing the wrong board, because when moving a message from one board to the next that particular date field is not updated.

Question: is there any date field that gets updated when a message is moved? Or put differently: how could I get a list of messages that have been moved from one board to another since a given timestamp?

Thanks for any help!

Edit: PS: it would be helpful to spell out on this page what exactly updates the last_publish_time field: does updating a product assocation/user tag/label attached to the message update this field? How about moving the message to a different board? The reason I went with conversation.last_posting_activity_time is that it is the more recent of:

• the last post time (equivalent to the conversation.last_post_time constraint)
• the last time the topic message was published (the last time a non-draft edit was made)

Which means I can also use it to update some summary metrics attached to a message (e.g. reply count).

So, does moving a message not count as a "non-draft edit"? It should, shouldn't it?