I ran the program IntMultCRACRA with your inputs <7306>12 * <A0A2>12 and got the following partial products that have to be summed up to obtain the shown product:

B 0 5 1 0 // pp[0][4..0]
B B 0 5 1 // pp[1][4..0]
B 6 1 6 B // pp[2][4..0]
0 9 1 A 8 // pp[3][4..0]
-------------------------------
0 9 1 A 8 B 1 0 // p[7..0]

Computation of the partial products:

<7306>12 * A = <B,0,5,1,0>12
<7306>12 * 0 + <B,0,5,1>12 = <B,B,0,5,1>12
<7306>12 * A + <B,B,0,5>12 = <B,6,1,6,B>12
<7306>12 * 2 + <B,6,1,6>12 = <0,9,1,A,8>12

About the red rectangle: You have to apply function alpha when you reach the most significant digits, i.e., in your red rectangle where we have i=1 and j=3=N-1, you have to compute the following

sm = xin * yin + pin + cin
= x[1] * alpha(y[3]) + alpha(pp[0][4]) + cp[1][2]
= 0 * alpha(7) + alpha(B) + 0
= 0 * alpha(7) + alpha(B)
= (11<(12/2) ? +x : +11-12)
= +11-12
= -1

and with this, you obtain

cp[1][3] = -1
pp[1][3] = 11
pp[1][4] = gamma(-1) = 11

About the green rectangle: Here we have i=3=M-1 and j=3=N-1, and we therefore compute

sm = xin * yin + pin + cin
= alpha(x[3]) * alpha(y[3]) + alpha(pp[2][4]) + cp[3][2]
= alpha(7) * alpha(A) + alpha(B) + 0
= alpha(7) * alpha(A) + alpha(B) + 0
= -5 * -2 + -1 + 0
= 10 + -1 + 0
= 9

and with this, you obtain

cp[3][3] = 0
pp[3][3] = 9
pp[3][4] = gamma(0) = 0

recall

alpha(x) = (x<(Base/2) ? +x : +x-Base);
gamma(y) = (y<0 ? y+Base : y);

Does this help?