Use changing variable to define range in loop

I would like to extract multiple ranges within a range on a spreadsheet. The number of rows always changing. This is what I'm aiming to do. The start row and the number of rows will always be different.

var sourcesheet = ss.getSheetByName("sheet name");
var nameRowN = starting rows already in an array
var sor = number of rows in each array already calculated and put in an array

 var ranges = [];
   for (var m = 0; m < sourcesheet.length; m++) {
   ranges = sourcesheet.getRange(nameRowN[m],5,sor[m],29).getValues();
   }

So ranges should include multiple mini arrays. The for loop goes through m, then m+1 and so on.
Am I on the right track? Is that possible to achieve what I'm looking for this way?

Edit: I can get the range outside of the loop and replace m variable:

ranges = sourcesheet.getRange(nameRowN[1],5,sor[1],29).getValues();

If your goal is to iterate through all rows with contents - you can use the method getLastRow().

Sample:

var lastRow=sourcesheet.getLastRow();
for (var m = 0; m < lastRow; m++) {
  //do what you want
}

Another possibility would be to use getDataRange() in conjunction with getValues() and length.

Sample:

var rangeLength=spreadsheet.getDataRange().getValues().length;
for (var m = 0; m < rangeLength; m++) {
  //do what you want
}