LLMs came some years after Watson- GPT 1 came out in 2018 (and was completely useless towards this goal), and Watson was developed mostly between 2005 and 2013

Ok, I suppose they might still have used the idea of a language model (LM) which has existed for much longer (Wikipedia says 1980). But the only difference would then be the use of transformers, which I understand is what the "L(arge)" refers to.

Side note. The terminology seems a bit confusing. Wikipedia says "LLMs are artificial neural networks following a transformer architecture." It's a bit strange to call it LLM then and not "Transformer-LM", imho.

If you take a dense (fully connected) neural network and take away edges, you can end up at the transformer architecture. Perhaps IBM just used fully connected networks and an insane amount of computational power and used the transformers without even knowing it (?)