The Assignment Panel not only allows you to make firm assignments, but also so-called Tentative Assignments by clicking on Tentative Assign. The assignment will be made, but there will be a ? after it to indicate that it is tentative. This allows you to make a provisional assignment and in a sense mark an assignment as less sure than a proper assignment. It is also possible to make several tentative assignments to one resonance. You may, for instance, face a situation where you have narrowed something down to two possibilities, but cannot distinguish between these yet. In this case you can make two tentative assignments – that way your peaks will be marked accordingly, and you can easily eliminate one assignment at a later stage and make a proper assignment. I find this helpful in order to minimise the amount of loose paper notes I have to keep – instead the information on provisional assignments is saved safely within the project.