Some comments: When numbers started being used, the dominant tactic of the day was the 2-3-5. (yes, that’s 2 def, 3 mids and 5 att).
1=keeper
2/3= R/L FULL back
4= R Half Back (4 is NOT lefty, never was)
5= Center Half
6= L Half Back (hence Brazilian wing-back)
7= Right Wing
8= Inside Right
9= Center Forward
10= Inside Left
11= Left Wing

When tactics evolved, you can see how the numbers transitioned:
2 and 3 became the side backs (because the 5 was pulled back) but we still call that position Full Back (although they defend less than the central defender – or half-back).
5, then 4 or 6 were pulled down to central defense (first one, in a 3-2-5 tactic, then two in a 4-2-4), so 5 was always a central defender, and 4 or 6 is the other defender (in Britain 5,6, in Europe 4,5). However, in Argentina, 4 and 6 are the DC, and 5 is a “true” half back (what we today call holding midfielder), and in Brazil the 6 moved wide left for a wingback role.
7 and 11 were so iconic and recognizable as wingers, that they stayed as R/L Mid.
8 remained in the middle, but is pretty unspecific, as tactics evolved more and more.
9 remained the goal scorer, and 10 is still the man!

Cheers!