You're always going to run into a person, in any walk of life, who is in a position of "authority" but is not as intimately aware of the details as you are; It might be a gate agent, a boarder guard, a manager at work, or your mother-in-law.

If a GA asks for the passport, why not just show it to them? If you don't have the patience to educate the person, and need to vent here about the whole process, it would save you a lot of stress. We still need to have the passport in our possession when we use Nexus / GE.... So why not just show the passport?

When I still had the paper I-94, I never had issues when I simply explain to the GA that 'I am on a TN-type visa which allows for multiple entry. Please do not take the I-94'; I've had some minor pushback but state I'm willing to accept the fallout from CBP during my next entry (SYM's answer to write on the card with red pencil is brilliant!).

What I've had the most difficulty with in the past, is the entry into the US from non-CDN ports. The 1st line CBP does not have the TN info available on his/her screen which automatically kicks you to secondary for not "having the proper paperwork" - which isn't necessary for the TN. But as the 1st line screener they can't physically see the specific requirements on their screen I get kicked to secondary - happened in LAX, SFO and IAD. So I wait in secondary for an hour or two, only to have my passport handed back without comment and I'm free to now attempt to re-book my connection.

Nexus / GE is worth every penny just to bypass the inefficiencies of the crossing-boarder systems (and avoid that infuriating secondary....)