https://www.vegascreativesoftware.com/us/upgrades-for-vegas-pro-and-vegas-movie-studio/

https://www.vegascreativesoftware.info/us/forum/vegas-pro-price-watch--109642/?page=5#ca744069

Please note that there may occasionally be some confusion regarding update vs. upgrade. An upgrade is not free and it will take you from one numbered version to the next (or a later one), i.e. 16 to 17. On the VEGAS product pages "you can upgrade [to the latest version] at a reduced price with a previous version or other authorized product. Please have your login details or serial number ready."

Updates are free new builds within the same version number. So if you update your VEGAS you get a new build, not a new version. (We may at times forget to make that clear.)