John DeLorean left GM to start his own car company in part because he believed automotive manufacturing to be unethical in terms of "model years". Any defects found, or improvements devised, were held back until the next year. This helped create demand for the newer "improved" models, but that meant continuing to build cars with known defects. On the DMC-12 manufacturing line, parts and processes were changed continuously. (The published DMC wiring diagram is considered to be a "suggestion" lol.)
Of course, there are practical reasons to do this: when you order a new knuter valve for your '83 Toyota Crapola, it needs to match. Making changes mid-year complicates the supply chain and ambiguates the service manual. However, in the 21st century, the service manual can be electronically distributed and updated on-the-fly, supply chains are streamlined, and technical data is instantly available. Tesla can look up your VIN and tell you exactly how it was built, and they don't seem to be shy about making mid-year changes.
With automotive functionality increasingly residing in software, the practice of holding back improvements seems even more unethical than ever. Since Tesla regularly delivers automatic OTA updates, it makes me wonder why we even refer to "model years" at all anymore.