You’ve had kerf compensation figured out ever since before you made that tutorial. But if you change materials you’ll have to make another adjustment to your drawing (unless, of course, the new material coincidentally yields a similar “enough” kerf).
If you know the kerf, and then compensate for it, the parts will come out the right size. Tests aren’t really necessary once you know the cut parameters (speed, power, frequency, focal distance) and the kerf width for the material you’re cutting. The only caveats to this are the small radiuses in the corners and the taper of the edges.
A link to the tutorial that Jules wrote, in case anyone reading this thread hasn’t seen it yet…
OK, if you want to get technical... (click for disclaimer)
There are a couple more caveats, the material has to be consistent enough that the kerf stays the same size throughout the cut, the machine’s laser output and motion has to be consistent too. Parts that start on fire or melt as a result of being cut also won’t necessarily come out the right size. Thermal expansion may technically come into play if ambient temperature fluctuates. Acts of god, lost steps, inaccurate tuning, time/gravity disruptions, and/or black magic may negate this rule. “Rightness” of resulting parts subject to stacking errors introduced by inaccuracies with the machine, the kerf measurement, the final part measurement, and rounding when converting units or interpolating tool paths.