When running a report and choosing your options for categories that contain a high number of options, you will only be able to see a set amount of choices. In order for the system to be responsive and load quickly, the dropdowns have been designed this way for better optimization.
For Example, if you have a high number of products, machines, users, resources, etc., to choose from, you may initially only be able to see the options beginning with "A" for the alphabetized selections. However, you can begin typing in what you are looking for and the system will populate the option for you.