> If they wanted a trademark, that needed to appear on copy from day 0. The paper is titled: "Improving Language Understanding by Generative Pre-Training" and not "Improving Language Understanding by Generative Pre-Training (TM)"

While the (TM) is useful to alert people to your trademark claim, you are not required to use it to establish your trademark. Simply using a unique mark to identify your goods or services and being the first to do so is enough.