I'm sorry, I don't understand. If someone says to me "Three of the numbers in the report were inaccurate" (an observation) that's a lot more helpful to me than "Your work is sloppy" (an evaluation). Did you have something else in mind?
"3 numbers were inaccurate" (just an FYI for next time, no big deal)
"3 numbers were inaccurate" (and I am annoyed that I had to deal with the consequences, please ensure it doesn't happen again)
"3 numbers were inaccurate" (but I understand the pressure you were under and the volume of work you had, so I don't see it as an ongoing problem)
"3 numbers were inaccurate" (and I see it as part of an ongoing, worrisome pattern of sloppy work coming from you, and I expect you to correct it)
Sometimes the recipient of the message really does need the speaker's evaluation, not just the bare factual observations, to put the message in proper context. "My order took 4 days to arrive" is a lot less useful than "Thanks, my order only took 4 days to arrive" or "I had to wait a whole 4 days for my order to arrive".
Personally, I don't get it either. No one I'm frustrated with seems to understand that if I tell them in an unhurried, matter-of-fact way. They may say that they prefer me to express frustration that way, but it gets no results. I don't see the appeal.
The magic of NVC comes from the recipient empathizing with the person making the request.
I genuinely have no idea what this means. What are you trying to say here? So I can be in any feeling except frustration when I'm conveying that I'm being frustrated? This sounds like snake oil.
And, in fact, people can be different in different scenarios.
In a work scenario I'm going to respond best if you're bringing up something I need to improve in a constructive way, with feedback that is actionable on my part, and doing so fairly dispassionately. "Hey Z. Here's what happened and how/why it was incorrect. Here's how you can make up for it/do better next time. No harm, no foul as long as you do better in this one area and keep rockin' it everywhere else."
But I need my wife to tread more lightly for some reason. Being dispassionate would be perceived by me as uncaring in that scenario.
In my experience there are two types of coworkers: those that respond well to BS (read: couched language) and those that don't. You just have to recognize who is who.
Often a speaker doing this feels that the sheer number of data points makes their strategy (that they will argue for shortly after finishing their list of observations) all but inevitable. People who have interacted with such arguers get understandably defensive when shown a barrage of facts painting them a certain way.
In the presence of a pattern of behavior, one example followed by every means necessary of keeping the offender on your side while building a strategy should be enough if the pattern is real and the offender has good intentions.