Transfer Information from one sheet to another

Use variants of this array formula:

=IFERROR(INDEX(Jan!B:B,SMALL(IF(Jan!$D$7:$D$13>0,ROW(Jan!$D$7:$D$13)),ROWS(D$6:D6))),"")

in D6. Copied down.

Array Formulae are a little different from ordinary formulae in that they MUST be confirmed in the FIRST CELL ONLY by pressing CTRL+SHIFT+ENTER to activate the array, not just ENTER. After that, the array can be dragged down as normal, to cover the desired range.

You will know the array is active when you see curly brackets { } - or "curly braces" for those of you in the USA, or "flower brackets" for those of you in India - appear around the outside of your formula. If you do not use CTRL+SHIFT+ENTER you will (almost always) get an error message or an incorrect answer. Press F2 on that cell and try again.

Don't type the curly brackets yourself - it won't work...

I used a non-arrayed version.
In Col G of all the monthly sheets, in G7 copied down as far as you think necessary (I copied down to row 30)

=IF(F7>0, MAX($G$6:G6)+1, "")

You can hide that column after you create it.

Then in "Amt Due", in D7 for example copied down

=IFERROR(INDEX(Jan!$B$7:$B$30, MATCH(ROWS($D$7:$D7),Jan!$G$7:$G$30,0)),"")

I completed the "key" or "dummy" columns in the monthly sheets and did the formulas for January in the Amt due sheet.