WM-D6C serial numbers and more

I haven't figured out the prefix letter either (E=Europe?) but I have seen one serial # sticker that had a 'Y' prefix.

 

Never seen these prefix letters on serial numbers either on any I have or worked on. @Deb64 has probably seen and restored more D6 and D6C units than most of us. I wonder if she knows the derivation.

 

I have seen one or two D6Cs with prefix letters in front of the serial number but I have no idea why they were used.

 

You are right, the label looks more like the serial number label in my WM-702 than the WM-EX900:

 

Wasn’t the E sometimes used as Tourist indicator in the service manuals?

 

What's a "Tourist indicator" ?

 

" Unfortunately, there is no sticker in the battery compartment so I can check the serial number. "
It's UNDER the battery compartment, visible only when you remove the holder.

 

On those early PCBs with the 20068 Dolby chip, they appear to me to be brown on the component side but green on the solder side. Is that right?

 

Sometimes Sony indicates that a model is meant not for JDM (Japan Domestic Market) in the service manual. I can’t find an example right away with tourist in it, here is one with E:

I don’t believe we can follow this logic though, as it could mean labels with AEP or UK could exist too.

 

Found on that indicates E and Tourist are not always one (https://walkman.land/document/108/Sony-WM-EX900-Service-Manualpdf):

 

I'm still trying to find the serial #/dates of the transition from brown to green PCBs and the same for the Dolby chip change (20068 to 20218).