If I understand correctly, you're starting with the data set you have shown, minus the A and B columns. Depending on what they are supposed to contain (you really have shown just an abbreviated version), here is one way to add them:
data want;
set have;
by trt notsorted;
if first.trt then do;
A + 1;
B = 1;
end;
else B + 1;
run;
Even if this isn't the right result, you will probably need some variation on these tools to get what you want.
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