I don’t see why many people deny the fact that they are most likely communicating with a thoughtform. I believe it could be because it makes people feel like they are less credible or something along those lines. I have noticed that thoughtforms have been given a negative connotation due to imposters. This is a belief that must be broken. Thoughtforms can be good, they can be bad, and they can be neutral. The usage of thoughtforms is also very common and very handy.
The reason why I say people could most definitely be working with a thoughtform is because of the very reasons you’ve stated. People have speculations and ideas about beings that they end up believing (even though that belief may not last forever). This would result in various thoughtforms of a being. It would explain why although people do get similar results, sometimes completely the same, there are also details that completely clash and even oppose the experiences of another. And sometimes the being is completely different in general from the experiences/ideas of someone else.
Also: I really dislike when people tell others that their questions about the background of beings doesn’t matter and/or that it doesn’t help. First of all: if someone asks, it matters to them. Second: these questions are needed and should be asked! We do it every time with our own species, our planet, and the universe in general. This is the point of growth, evolution and expansion. Ask questions. Discover truth. Gain knowledge. Yes, it’s great and all that they can help you- of course, go for that. But these are questions that shouldn’t be shunned. From my own experience, understanding the beings you work with can better expand your knowledge and awareness of them, it can, in fact, deepen your relationships with them, and also help you learn more about the life that exists in this universe. It does help with learning what is real. Now, I’m not saying you need to know every single thing about them and their background. But better understanding them? Definitely.
We can’t even compare our knowledge of our own people with the knowledge a metaphysical race of beings- who are more evolved than us- has of their own kind. Chances are (and this is the case majority of the time) that they actually do know their history, even our own. So why can’t we? Knowledge is power.
As for Tiamat: she does indeed appear in various cultures under different names. She is the mask/personification given to the primordial force of the ancient chaos. So you will come across many variations (aka thoughtforms) of Tiamat, but all ultimately represent the same concept/energy. As time goes on, I see that more variations based on the ideas of others are formed.