Distribution of scores of 2 strong pairs in 7-table Mitchell

In the complete Mitchell movement we have 7 rounds, thus the top on a board is 12 MP.

score card 1: pairs 1 and 2 are the strong pairs
PairContractRes.Score  MP  
NS EW NS EW
13 NT   +1 +630  11
23 NT   +1 +630  11
33 NT   C +600  4
43 NT   C +600  4
53 NT   C +600  4
63 NT   C +600  4
73 NT   C +600  4
8  - 1 -  -6301
9  - 2 -  -6301
10 - 3 -  -6008
11 - 4 -  -6008
12 - 5 -  -6008
13 - 6 -  -6008
14 - 7 -  -6008
First let us look at the case where the 2 top pairs play in the same subgroup, say NS. Then each score card contains 2 times 11 and 5 times 4 in the NS column, therefore 2 1's and 5 8's in the EW column. The total score (for simplicity we assume 1 board per round) will be:

for the 2 strong pairs:  7 x 11 = 77
for the other NS pairs:   7 x 4 = 28
for all EW pairs: 2 x 1 + 5 x 8 = 42

In total 2 scores of 77,
         5 scores of 28,
     and 7 scores of 42.

score card 2: pairs 1 and 9 are the strong pairs
PairContractRes.Score  MP  
NS EW NS EW
13 NT   +1 +600  12
23 NT   -1 -100  0
33 NT   C +600  6
43 NT   C +600  6
53 NT   C +600  6
63 NT   C +600  6
73 NT   C +600  6
8  - 1 -  -6300
9  - 2 -  +10012
10 - 3 -  -6006
11 - 4 -  -6006
12 - 5 -  -6006
13 - 6 -  -6006
14 - 7 -  -6006
score card 3: pairs 1 and 8 are the strong pairs
PairContractRes.Score  MP  
NS EW NS EW
13 NT   C +600  6
23 NT   C +600  6
33 NT   C +600  6
43 NT   C +600  6
53 NT   C +600  6
63 NT   C +600  6
73 NT   C +600  6
8  - 1 -  -6006
9  - 2 -  -6006
10 - 3 -  -6006
11 - 4 -  -6006
12 - 5 -  -6006
13 - 6 -  -6006
14 - 7 -  -6006
Next consider the case where one top pair plays NS and the other EW. Now most score cards will contain two 12's, 2 zeroes, and 10 6's. Except for the one board where the 2 top pairs meet each other, this score card has all 6's. The total scores in this case are:

for the 2 strong pairs: 6 x 12 + 6 = 78
for all other pairs:    6 x 6  + 0 = 36
In total 2 scores of 78,
    and 12 scores of 36.

We can choose the pair numbers of the 2 strong pairs in 14 x 13 / 2 = 91 different ways. Of these 91 combinations there are 42 (i.e. 7 x 6) where they play in the same direction and 49 (i.e. 7 x 7) where they play in opposite directions. All together we have the following distribution of possible scores (In brackets the MP scores converted to percentages)

49 x  2 =  98 scores of 78 (= 92.86%)
42 x  2 =  84 scores of 77 (= 91.67%)
42 x  7 = 294 scores of 42 (= 50%   )
42 x  5 = 210 scores of 28 (= 33.33%)
49 x 12 = 588 scores of 36 (= 42.86%)