There was a person  named Charles G. Barkla who named the shell as k,l,m,n 
this was because He noticed that atoms appeared to emit two types of X-rays. The two types of X-rays differed in energy and Barkla originally called the higher energy X-ray type A and the lower energy X-ray type B. He later renamed these two types K and L. he then came to know that k type x ray energy and also produced by inner most shell therefore he named the shells k,l,m,n .

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They keep k,l,m,n, because that are scientists names 
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