Hey there!
Apologies for the delayed reply. Yes, the dimensions in Easel Cabinetmaker are all external unless otherwise noted.
We typically For blind dado construction, we factor in a tolerance of 0.03" by undersizing the rabbets by 0.015" and oversizing the dados by the same amount. Our testing has determined this to be a sufficient tolerance for plywood to produce a snug but not overly-tight fit.
It is important to note that the exact geometries and dimensions for rabbets and dados are calculated when the project is nested. If your material is not exactly 3/4", we recommend measuring the material with calipers and entering the exact thickness in the material fields in Easel Cabinetmaker. If the project has already been nested, it can be re-nested with the appropriate material thickness by selecting “Replace existing workpieces.” If you nested your workpieces with the material set to 0.75", and then change the material thickness of the workpiece in Easel (without re-nesting), the joint quality of the end product may be impacted.
I’m sorry we didn’t get back to you sooner. Thank you for sharing your questions and feedback! Please reach out if anything else comes up!