Slowakische Kassettensite mit allen Einlegern

[2245]

So we can't tell the difference, which were from 1992 and newer, made in Germany and Luxembourg?

Seems so, never caught a difference to tell them apart. So all we can say is Germany or Luxemburg.

I think the Japanese tapes in the pancakes may have been stored for a few years, like the ones for C150 cartridges. So this won't be entirely accurate.

I don' think so, storing is very costly (manpower, energy and space) so just in time production became industrial standard about two decades before 2007.
Especially for low margin mass products! Cost cutting was very important for Recording Media with high cost pressure since the late 80s.
In the case of the much rarer C150 tape it could have made some sense to store some stuff, because they knew they would not get such tape after ceased production.
If you think about the numbers of cassettes that were produced in a month, it's impossible to store enough tape for a full production in the next year or even futher away. All these old stock theories are total baseless in my opinion.

And the Mikumagawa plant was still active in coating audio tape in 2007. Sadly there is no such "site report" for 2008 and later.
From the 2008 CSR report for the year 2007:
   

It's highly likely that that they ceased the japanese tape production at the Mikumagawa plant by end of 2007 or in 2008.
In a fiscal report for 2007 TDK stated, that with shift of the sales operation for recording media to Imation in 2007 the whole media buisiness had to be reorganized. 
At the same time the tape made in Korea appeared on TDK Cassettes.
They already had stopped to make their own optical discs in Japan and USA in the early 2000s and in 2006 the last disc plant in Lux was closed too.
So most probably, beside of Blue Ray and Audio Cassettes (molding assembling) in Thailand TDK made nothing on their own after 2007/08.

The most recent AH/AG cassette is probably really 2002.

Possible... But in the 2006 STEREO tape test they claim that TDK stopped Luxemburg Cassette production in 2005.

And when TDK Germany was closed in early 2003 reports were that the production went to Lux.
But maybe they meant CD-R and El Colis, that were also produced in the german plant.
I too don't think 2005 is correct, my guess is somewhere between 2002-2004.

But TDK D Life On record for the US market, for example, also bought some Panggung cassettes.

Of course, these non TDK cassettes that were bought after the flood destroyed the Rojana Plant in October 2011 can be from 2011 and 2012.
All LOR cassettes made by TDK were from 2008-2011.