Congratulations, but I'm curious to learn why you are convinced that the dial is original? Have you dated the watch from the movement serial number? Is it a cal. 8521 or 8531?
Thanks, it has a cal. 8531, movement serial number dates it to 1959. I’m no expert on IWC Ingenieurs but have been collecting vintage watches for almost 20 years, and everything I’ve read and seen leads me to believe the dial is original. Here’s a link to an identical dial featured in a IWC forum thread: https://www.iwc.com/forum/en/discussion/12887/
Well, although I cannot be 100% certain, I do not believe that the dial, nor the lume on the hands are likely to be original to the watch. I have owned more than a few Ingenieurs over the past 25 years, including black dials, and a ref. 666 was my first "good" watch. I would never expect a 55+ year-old watch to have such bright and well-preserved lume, nor signatures on a black dial. Also, the Ingenieur signature is a later, thicker version. Here is the type of (finer) signature that is typically found on the earlier 666 dials: The lume plots on the dial are also suspiciously well-preserved, and "T SWISS T" was not typically found on the earlier dials. I would surmise that the dial and hands are service replacements, but I could be wrong. What is the condition of the case and movement? The black one to which you linked on the IWC forum is from 1964, so not a taut comparison.