Help with identifying age of guitar pedal
 

I was given a secondhand effects pedal by my dad several years back, which he said he was given secondhand in the early 1990s. It's a Japanese-made Tokai Metaldriver TMD-01, which appears to be a rare model today, and I use it when playing my guitar if I want distortion - it's still in good condition for its age. Most sources indicate the model to be from the early 1980s, but there seem to be variations of the pedal in terms of the white markings. Mine looks exactly like this, with the slightly more basic markings:

http://medias.audiofanzine.com/image...ver-531210.jpg

Some, however, look like this, and I'm unsure whether they're newer or older than my type. I'd be inclined to say newer, though I can't be certain:

http://files.effectsdatabase.com/gea..._tmd-1_001.jpg

So does anybody know what years my pedal was in production? I think it was first produced in 1980 but don't know when production ended (probably whenever they were ordered to stop making them due to their habit of infringing on patents).