Oh bhai… I will take the BUT out of it… There is no Shak here.. This is FACT. Human NATURE is such that we derive different meaning from single sources.
And once again, you not proscribing to Naats is your intepretation and understanding. By the way, just because Arabs do it, doesnt mean its right either… 
Muslims do this ALL the time. Why do you think there are so many different schools fo Islamic thought and philosophy?!?! Because Muslims are always interpreting their beliefs.
Do you think Muslims could live in the modern world without interpreting their religion to conform in some way with the changing world? For example, does Islam say a woman should be covered head to toe, just cover the head, or be completely hijab free? Different people have varying beliefs even though the examine the same literature. Does Islam allow music? Interprtation differs.
I dont want to be anything. Im only explaining to you that tolerance must be foremost in relgion. Because its not somthing you can ever be certain off no matter how much you try to fool yourself.
You should ask yourself why you want to be a Muslim… If you can answer that then im sure you can figure out why Ahmadis want to be Ahmadi. In fact, then you can answer why a Chrisitan would be Chrisitan a Jew a jew, and a Hindu a Hindu.
And the point of using the term Mehdi or Messiah is irrelavant. Christians derive many of their words from Greek translations of Hebrew text. Hebrew and Arabic have similar origns. Hence, its possible that some place in antiquity, the two words are the same.
And Koran or Quran is also irrelvant and I ask you to stick to the topic. The Koran was originally written in Arabic and there is no broad consensus on how it should written in English. And since you dont own the Arabic word, I dont care how you want me to spell it in English. Just to annoy you, I will contiue spelling it the KORAN. And if you dont want to confuse it for Korea, then you better read carefully.