Woo. Slow down. A bit of misinformation here.
First,
CARNAC does not look up metadata. It happens before metadata is looked up, and uses "filename, length, file type, and other details" to "fill empty database fields". Okay, database fields are metadata, but CARNAC isn't looking them up, just reading them from the file name. It happens when a file is first introduced to MC, during import, and is most useful when importing heavily structured video file names such as; "Marvel's.Agents.Of.S.H.I.E.L.D.3x02.Purpose.In.The.Machine.HDTV.x264-KILLERS.[tvu.org.ru].mp4".
CARNAC is much less useful for recorded TV programs, as the tag information comes from the EPG data, rather than the file name. In fact, MC will use information that it has from the EPG data to decide what to name the file. For example, MC will use the Season and Episode numbers in the file name, if it knows them at the time the file is created.
i.e. "Marvel's Agents of S.H.I.E.L.D - S03E01 - Laws of Nature.jtv"
It is the "Get Movie & TV Info" function that gets additional metadata for the program from TheTVDB, and that happens when the program is imported into MC, even for recorded TV. In fact, I don't know exactly when it happens for recorded TV. It could happen when the file is created, which is when it is "imported" into MC, or it could happen when the recording is finished, but most likely it happen sometime after being imported and before the recording finishes, when MC kicks off the TV maintenance function.
If we use the correct terminology, we might gain a better understanding of what is happening.
Next, since MC21.0.28 MC has been able to look up TheTVDB using just the Series and Episode names, just like EPG Collector has been doing for some time. Try it and see. For a recording that has no TVDB ID or Season or Episode number, but just has Series and Episode Name, run the "Get Movie & TV Info" function, it will return any match it finds (as long as TheTVDB actually knows about the program). It is still a bit crude and can be tricked, but it works. So having Season and Episode numbers in the EPG data is a little less important than it used to be.
21.0.28 (12/14/2015)
5. Changed: TheTVDB lookup can look up tracks that don't have a season or episode number and will now look up just by the episode name.
See the bolded blue paragraph in
this post, and read the following posts.
Now I can only do limited testing of this new functionality, because most of my EPG data now includes Season and Episode numbers supplied by EPG Collector. So testing it would be great, and if it isn't working properly, let JRiver know.
Also according to this document https://msdn.microsoft.com/en-us/library/windows/desktop/dd776338.aspx - Season data is in the Rovi data going to WMC users.
That Microsoft document is from July 2009. I doubt it is talking about Rovi data. I can't see any reference to the source.
That document refers to when Microsoft used Gracenote data, not Rovi data. Microsoft changed from using Gracenote to Rovi data in June/July 2015. The only test as to whether WMC users get Season and Episode numbers in Rovi data now is to run WMC and see, which you are doing. From what I have read, lots of WMC users aren't happy with Rovi data. Please let us know what you find.
Note that the additional Season and Episode number data is available from PerData, but as far as I know it requires additional functionality in MC to get it, which hasn't been implemented yet.