I noticed that it says "or" rather than "and" in reference to a binder and field guide. In previous taxonomy competitions I believe both have been allowed simultaneously; teams would be allowed to have a binder AND a field guide. Why the change?
I'm guessing the national committee wants to change the way ID events are done. I mean for biologic ID events it was always 1 sheet of notes and a field guide but they changed that with invasives because there was no field guide. I'm guessing they liked how the event turned out with the binder and want to change the strategy for ID events. The only events that used to have the field guide and binder were the geologic ID event and in 2017 they got rid of the field guide for rocks. Personally, I think it's a very interesting change to the rules because now teams have to decide which resource they want to use and how they are going to deal with the shortcomings of each resource.
Back in my day, I believe they were full binder events. I did Forestry, Entomology, and Herpetology with binders. In my senior year (2009), Herpetology was changed to ONLY a field guide, no binder and no note sheet at all. Note sheets were added after that, and then Invasives was a binder because there aren't any field guides that have everything you need for that event.
So it's changed around a bunch of times. Personally, I think binders are always better because you have to decide what information goes into it and part of the difficult of the event is preparation. That being said, I know some of the Bio ID events will base themselves off of specific field guides and defer to that one in the case of conflicting information, so it's probably a good idea to get the field guide anyway to help make your binder.