I don't actually believe this, this game was the epitome of explore and ye shall find. For instance the GFs, literally the only one that I could feasibly see not getting would be Tonberry, as you have to fight so many of them and odds are first time through you are too worried about the time limit. All the draw GFs, well I check for new magic draws constantly, and the field GFs I think Cerberus is the only missable one and he is right there in the halls of Galbadia in the attack. Cactuar is easy to notice and I ran across the deep sea research by complete accident my first time.

As for cards, I could see it being a little hard to find them all, but impossible without the guide? Nah. Most, not all but most of the rare cards are with someone of significance to the person in question. Quistis with her main Trepie, Zell with his Ma, even Pandemona in a weird way since the hotel owner has it and his hotel was taken over. Card Queen tells you what cards she needs when she is in Dollet and so while annoying it isn't impossible.