The new agents don’t use TMDB (or any source) directly, it’s our own metadata that uses TMDB data along with multiple other data sources. On the Plex item we store the id for all these sources which is how you can use these ids to link to our items but the data won’t be identical, it just means we’re using data from that source.
This is something we want too.
All the old legacy agents will get removed at some point which is why we’ve been nagging folks to change over - you can see this reply: Please do not switch off legacy agents/scanners without a way of adding my own metadata - #5 by hsousa