Look with Bulbasaur (plural) being in the episode likely evolving, there might be a chance that Ash's Bulbasaur will evolve. It's not a guarantee but it at least is a possibility for now (VA list could tell us if Bulbasaur will be in it, or at the very least Bulbasaur's VA if she shows up in the list, we could get Ash's Bulbasaur).
But I HIGHLY extremely doubt the hypothetical Ivysaur is then going to further evolve into Venusaur. Ivysaur at least makes some sense, but I highly doubt they'll give Ash a Venusaur THIS early plus I feel like they'd at least want to show us Ivysaur for awhile (IF it evolves).
The problem with poster being confirmation, is that we know multiple Bulbasaur are going to evolve into Ivysaur, and multiple Ivysaur are going to evolve into Venusaur. All the poster does is show us the line evolving from Bulbasaur to Ivysaur to Venusaur.
This makes sense given that when Ash's Turtwig evolved the title was basically "Turtwig, Grotle and Torterra" it wasn't saying that Ash's Turtwig was going to fully evolve. But it was a reference to Ash's Turtwig evolving into Grotle and Paul's Torterra.
Same here minus the title. A lot of Bulbasaur will evolve and a lot of Ivysaur will evolve. I very much doubt, we'll get two evolutions from the same Pokemon in a single episode, let alone Ash's Bulbaaur.
I mean don't get me wrong, the experience Bulbasaur possesses is probably more than enough to evolve twice, quickly if they really wanted to, but I doubt they'll just evolve Ivysaur immediately, I feel like it would take awhile, after all if they are deciding to evolve Ash's Bulbasaur, I feel like they would want to show off Ivysaur a lot. You know have Ash use it for quite a few episodes. Why evolve it immediately into Venusaur? I don't think the point is to ridiculously overpower Ash so soon.