I wouldn't know as I've only really discovered Q recently. The guys in the video seem expert at what they do, I've watched them a number of times now, and I'd say they're an excellent source of info.

My guess is that markers are not sequential. It may also be the case that they can be used multiple times to track different sets, and differentiate by context.

Also, I'm assuming it is "progress" based on the fact that it's a new message and it points to a Q post.