Python 2, 97 95 75 72 bytes
lambda a,b:(-1<a<=b<22or 0<a>=b-2<b<31>a+1)and(20<b-(b<30)>a)+(a<20<b)+1
Takes input as pre-ordered a,b.
Returns 2, 1, False for ended, in play, invalid.
Python 2,
TFeld
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