Please be aware that only files distributed by Mamedev (those available via the official GitHub) have been subject to the relicensing efforts.
If you maintain a derivative build please be aware that you will have to gain the correct permission from all contributors for any extra code you have in your build. Code that was distributed under the previous MAME license can not be included or linked to MAME from this point forward without being relicensed, requiring permission from all contributors to that code.
This applies to all derivative builds, including MAMEUI, MESSUI etc. so if you have a derivative build based upon that code you will need to either rewrite from scratch or obtain permission from all contributors to the code in order to relicense.