I guess this question is mostly for John Ehrman, but others may have insight as 
well.

For the same machine instruction format, there are sometimes two different 
HLASM operand orders used for the operands of instructions.  For example, LOC 
has HLASM operands in order 1,2,3 while STMCH operands are in order 1,3,2 and 
the machine instruction operands are in order 1,3,2:

LOC          R1,D2(B2),M3                 [RSY-b]
'EB'   R1   M3   B2   DL2   DH2   'F2'
0     8    12     16    20     32       40     47

STCMH    R1,M3,D2(B2)                [RSY-b]
'EB'   R1   M3   B2   DL2  DH2   '2D'
0     8    12     16    20     32      40     47

Here is a second example, LPD has HLASM order 3,1,2 while MVCOS has HLASM order 
1,2,3 and the machine operands are in order 3,1,2:

LPD            R3,D1(B1),D2(B2)       [SSF]
'C8'  R3   '4'    B1   D1   B2   D2
0    8    12    16   20    32   36   47

MVCOS     D1(B1),D2(B2),R3       [SSF]
'C8'  R3   '0'   B1  D1   B2  D2
0    8    12   16   20   32   36   47

Am I the only one to whom the inconsistency seems arbitrary?  Or am I missing 
some salient characteristic that explains the differences?

Peter
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