My professor told us a previous version of our textbook would be okay, but has now decided that it isn't?
I've been both in situations where I told my students &quot;I've looked at the 1st edition of the text and it's OK to use it&quot; and &quot;I've looked at the 1st edition of the text and it's not OK to use it&quot;. It sounds (unless I misunderstand your story) that your professor never looked at the prior edition and just assumed that it would be OK. I hope that &quot;never assume&quot; will be one of the lessons learned in this class by everyone, including your professor.
The professor tried to mitigate their mistake. (Other possible solutions might be to limit the topics of the guided inquiry to the material in the old edition, but that would not be fair to the students who do have the new edition.) Clearly, this creates a huge inconvenience for you (and the other people with the old edition), but also, more importantly, you're missing out on the material that's in the latest edition and is missing in the one you have.
My advice to you is twofold:

You're missing out on gaining the knowledge which is the goal of your being in this class and in school. You're not learning as much as the other students who have access to the current edition. Get hold of the current edition of the text book (buy it new, buy it used, rent it, download it for free from pirate sites, borrow from somebody). It may cost you, but the alternative is that you won't learn in this class whatever you've set out to learn.

Do not say anything to the professor. Nothing good is likely come out of it. The professor already knows that students who have the old text are inconvenienced. You have nothing new to say. The professor sounds very unlikely to change anything again, but also sounds like the type who might retaliate and dng your grade for complaining. If your school conducts course evaluations at the end of the semester, explain there clearly what went wrong.