[@VitaVitaAR] I dont think you understand. Mordred's specific origins within her legend dont matter. People within the Fate universe think that Mordred and Arturia are both male, their legend is essential similar to how it is in our world (with a few exceptions, Arthur never conquering Italy and various other details being different) 

I dont know where you are getting that its not like I describe it. Arturia knows who Diarmuid and Cuchulain are, and they her, even though that should technically be impossible. It is information that the grail has given her directly similar to how she knows modern language and most customs. Sigfreid for example knows that Sigurd exists because they are very closely related legends, basically being different versions of each other. Saber does not know who Sasaki Kojiro is because his legends does not relate to her at all and is in a complexity different cultural sphere. 

When you have two legends that are geographically very close, take place at nearly the same time, and have dozens of similaritys and identical themes to eachother its pretty obvious that the two legends are related to and influence one another, just like the swords Gram and Calburn are.

I dont see where you are making the distinction where you are willing to admit that the swords are related prototypes of each other, but the people who's legends are even more similar are not? If Merlin was summoned and Myrddin Wyllt was also summoned they would quickly recognize eachother as being related, even though they are from different legends. Same thing here is what I am suggesting.