Migrate and GUID?

I recently (last month) migrated my site from a dev server to the live site after archiving all files on the live site so that there were NO root-level existing files or folders. Things went well and the live site took on all the changes and improvements made to the dev site. Yesterday I was browsing through the database on the live site, and I happened to notice that many of the GUID values contained the URL of the dev site, INCLUDING some with dates in Feb and March of this year! Why is that happening and what effect will it have on the operation of the site?

Thanks for any suggestions!