I am not even sure what to make out from that question.
Basically, mangaka would first set their works to be targeted at their audience, which are indeed Japanese. This is perhaps for profit, or for interest. At this stage, the world does not really know of it (many manga dies without being translated or noticed).
The good ones get a good fanbase, and starts to leak to the outside world. This is what you would get usually. Whether the author knows of this is not important. At this stage, even if the author do know that the manga is getting global attention, to change his audience base towards that would be an insane, if not suicidal attempt. It was due to the idea that was targeted at the Japanese audience that got him so far, to abandon it after it got famous is more than foolish. It could easily lose all its fans, both the Japanese and global side, as well as make his reputation go down the drain. Furthermore, while it seems like there is a large fanbase, it is not profitable for manga to be targeted globally. Even if a famous manga artist wants to try shifting global, he would have to look for some company that is willing to translate his manga so the global market can read it. It is too costly and risky. So whether the mangaka does know of his global fanbase does not really matter in any way. If you simply mean if he knows he is famous, then here's a quote for you.
Translated from what I remembered by the author(I think this quote is directed to the Japanese fanbase when he said it):
When I started my manga, I typed the name "Letter Bee" into the search bar. There were almost no results. Now, when I type "Letter Bee", I see many results with regards to my manga. That made me feel accomplished.
They would do their own research if they do mind, but it should not affect their works much I think.