Correct. If the dado is fairly deep I use the step turret on the plunge router to take multiple passes. I went this way since it offered me the versatility. I sometimes over-focus on making a tool or jig serve multiple purposes in exchange for the space it takes up in the shop ;-)A fine jig, to be sure. Executed flawlessly as we have come to expect from you!
I have a question - I think the rabbet for the collar is a neat idea. Just wondering why go through the hassle of attaching a collar instead of using a dado clean out bit? Answering my own question: If your doing 3/4" +/- dados the dado bit s the way to go but, since they usually don't come in less that 1/2" diameter, you can't use it for today's "less than 1/2" plywoods". The collar method will work for dados as small as you have a straight bit for. Sound right?
I studied my dado use where such a jig would come into play and 3/8" was what I chose as the small dimension. This lets me do most 3/4" plywood dados in two passes. I felt that building for a 1/4" bit (the dimension of the ledge and zero edge would change) left me making lotsa passes for most things. Smaller dados are usually on smaller things so this big-ole-whompin' jig would be awkward there anyway. As usual we facotr in what we can and take our best shot