I was referring to the downstairs WC. In the first drawing you posted, if you just delete the upstairs bathroom completely, the dry vent path for the downstairs WC isn't correct. A dry vent has to come off the upper half of the drain, and it has to rise at least at a 45 degree angle until 6" above the flood rim level of the fixture. So the WC dry vent can't go horizontal under the floor to reach the 3" stack you have.
Your last drawing is fine; the 3" stack on the right has the same problem as far as dry venting the WC, but the dry vented shower (assuming its vent complies with the above rules) will wet vent the WC. In fact if you want to reduce the number of dry vent take offs, you could do it like in the drawing below. Upstairs the dry vented lav can wet vent both the upstairs shower and the upstairs WC. In fact downstairs you could eliminate the shower dry vent if you rerouted the lav drain to join the horizontal line between the shower and the WC; then it would wet vent both the WC and the shower. [The dry vented fixture wet venting the bathroom group can't be the third or later fixture, it has to be one of the two most upstream.]
Note that the vent takeoff for a sink or a shower (or anything with an external trap) has to happen before the drain (trap arm) falls more than one pipe diameter. On a wet vent, that vent connection is where the fixture drain joins the horizontal drain that is carrying the dry vented fixture.
Cheers, Wayne
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