Tube noob, still learning about tubes here. I got another batch of vintage tubes, a couple hundred I’m guessing. I’m using the Philips Factory Valve Codes pdf, which was a great find. Enjoying the research and general quest for knowledge. My question; With the bottom row of codes being D1K, is it 1961 or is it 71? I can see this being a common issue when identifying these things. The entire code is DJ2 D1K Does the ‘2’ batch number somehow help narrow it down like on pre 1956 tubes? Google seems to indicate Valvo in Hamburg being in operation both in ‘61 and ‘71, so no help there.