I have not read any convincing and satisfactory justification on 'how the numeric value for the alphabets has been assigned'.

But calculating the values for any Name, as per the real spelling and the sound, we can get Name Segment.

If checking and comparing the Name Segment with 'Ever wondered why some male behaves like female & female behaves like male?' (members only), one can realise the amazing influences of the value of the Names.

So, let the honourable persons like scientists, scholars, researchers, rationalists, mathematicians, skeptics do research in this subject.

Till then, let us not worry about 'how it has been assigned', but try to use and implement it in our life, to lead a successful life.

Please refer: Numerological Value of Names, Numerological Value of Sound, ready references