OK - It's easier to explain this by "showing" someone, but I'll try to do it in writing, so here are Jared's "8.5 Steps to cut a multi-opening double mat":
Step 1- Get your two pieces of matboard first, accurately pre-size your top mat first, and make sure your bottom mat is slightly smaller (1/2" - 1") than the top mat, all around.
Step 2 - Using some forgivable, removable ATG or tape, stick the two mats together (yes - before you even cut anything!) and mark the exact position of the smaller bottom mat, stuck to the back of the top mat, for future re-alignment (Step 8).
Step 3 - Using the front mat as your outside edges - accurately measure and draw all your openings in the bottom mat.
Step 4 - With both mats still stuck together - cut the openings out of the bottom mat (from the back - always make sure the opening is under the slideway of your matcutter!). No need for a slip mat in this case, because the top mat will perform the duties of your slipmat.
Step 5 - After you have cut all the openings for the bottom mat, seperate the two mats - removed the fallouts - and inspect the bottom of the front mat - you will notice scorelines from the blade, lining up where all the bottom mat openings were cut.
Step 6 - Use these scorelines on the rear of yout top mat, as reference guides, to help accurately measure and draw new parallel guide lines (1/3" or 5/16" which ever you prefer to use) outwards - around each opening.
Step 7 - Cut these windows out of the top mat, from the back (use a slip mat now!)
Step 8 - Re-stick your two mat layers back together (permanently this time) using the "alignment marks" you made at Step 2.
Step 8.5 - Post a Xmas Card to Jared!
Cheers,
Jared
Edit Note - In the 25mins it took me to write this response - 4 other responses were made.... Grrr..... !!