thread numbers and moved threads

Okay, this is puzzling. When a new thread is started, it gets a number. What happens to that thread number when a thread is moved to a new forum? Is that number recycled, and all the later threads cycled down a number? That would certainly screw up links. Or is that number reserved somehow?

In the old board, a thread would be locked in the original forum and retain as a placeholder. There does not appear to be the same locked threads in vB. How does this work?

Curiousity abounds. I noticed once or twice when returning to a forum that a thread would be highlighted that did not seem familiar, like I had not read it. Nobody else uses either my home or office computer, so it is not likely someone else read it in my stead. I am curious if the above question could be an explanation, or if it’s just my memory playing tricks on me.

Thread Ids and Post Ids remain unchanged after a thread is moved to another forum.