majorrptList = rpt << xpath( "//OutlineBox[contains(text(),'Standard Deviations')]" );
returns a list of the pointers to all of the different Outline Boxes in your journal, that have the title "Standard Deviations".
The returned list is:
{DisplayBox[OutlineBox], DisplayBox[OutlineBox], DisplayBox[OutlineBox], DisplayBox[
OutlineBox], DisplayBox[OutlineBox], DisplayBox[OutlineBox], DisplayBox[OutlineBox],
DisplayBox[OutlineBox], DisplayBox[OutlineBox], DisplayBox[OutlineBox], DisplayBox[
OutlineBox], DisplayBox[OutlineBox], DisplayBox[OutlineBox], DisplayBox[OutlineBox],
DisplayBox[OutlineBox], DisplayBox[OutlineBox], DisplayBox[OutlineBox], DisplayBox[
OutlineBox], DisplayBox[OutlineBox], DisplayBox[OutlineBox]}
If you want a count of the number of the Outline Boxes, you would need to do something like
numOutlineBoxes = N Items( rpt << xpath( "//OutlineBox[contains(text(),'Standard Deviations')]" ));
Looking at the remainder of your JSL, it appears that you are confused with how to deal with the 20 different Standard Deviation Table Boxes. You seem to want to take the count of the number of Standard Deviation Outline Boxes and somehow retrieve all of the data from all of the 20 Table Boxes all at once. Your syntax is also incorrect, and returns an error message. What I believe you want is:
sumFit = majorrptList[1][Number Col Box( 1 )] << Get as Matrix;
Which returns
[3.67530167633204, 3.67530167633204, 7.01812976988444]
Which comes from the 1st Standard Deviation Outline Box in your journal

You seem to want to use numOutlineBoxes in your reference, in an attempt to somehow get all of the data from all of the Table Boxes. However, since the value of numOutlineBoxes is 20, what running
numOutlineBoxes = N Items( rpt << xpath( "//OutlineBox[contains(text(),'Standard Deviations')]" ));
sumFit = majorrptList[numOutlineBoxes][Number Col Box( 1 )] << Get as Matrix;
what you get is
[0.00401248052954899, 0.00401248052954899, 0.0399901237806931]
which are the values from the 20th Standard Deviations Outline Box

It appears that you are attempting to run before learning to walk. I suggest you slow down and take the time to read though the Scripting Guide to gain a better understanding of JSL before you take on such a large project.
Jim