Base buildings required in calculator & WaterSense labelled?

My understanding of the prereq / credit separation is this: Prereq: You must meet the WaterSense requirements and provide calcs/documentation for all fixtures that are within the project scope, at a minimum. Credit: IF you want to pursue points, you must include all fixtures that the users are actually using, whether they're in the scope or not. Base building fixtures that are not in your scope are not required to meet WaterSense or flush/flow rates, but are required to be in the calculations.
If you do NOT want to pursue points (e.g. the base building existing fixtures are old and bring your overall % savings down), you just don't document or pursue that credit at all.

I don't believe cutsheets are required. In many cases, I doubt you'd be able to determine exact makes/models just by visuals, anyway. I have, in some cases, had photos as backups. If it's a case where you have access to the original fixture info, I'd have it handy just in case; it's safest to only supply the documentation that the form tells you to provide. In most cases, the reviewers don't want extra info to sort through unless required.

What about the standards for appliances and process water use?  Specifically, cooling towers in the case of my current CI project.  If the cooling tower(s) are part of the base building and not the projects scope of work are they exempt from meeting the standards listed in tables 2 and 3 of the reference guide (page 90)?

Nope. It should only apply to what's in the project scope.

Dear all, I received the preliminary comments from the LEED reviewers for one of my CI projects, and we have been awarded the Water Efficiency credit as well. Based on the declaration, only the plumbing fixtures inside the LEED project boundary will be accounted for the calculations. If you declare the entire floor as your project boundary, then the project team needs to evaluate all plumbing fixtures whether these are new or existing.