When an NCO arrives at a new unit, where does it say they do not have to provide previous evaluations or place them in counseling packets?

Where does it say they do? Transferring units is supposed to be a fresh start. Otherwise no one would ever recover from that stupid mistake they made when they were young.

During my initial counseling with my NCOs, I usually ask for on the front side of their last three NCOERs, as this will help us both develop an understanding of previous assignments, primary and additional duties, etc. The back side of the NCOER isn’t necessary, but it can serve as a good professional development tool further down the line when discussing professional growth, good NCOER writing techniques, and other things.

SSG Doug Mckee,
After being a Personnel Officer for almost 7yrs I’ve routinely found myself in a very similar situation. As a young AG Officer learning and perfecting my craft I can tell you that I've made some mistakes that I learned from and told myself I would never allow to happen again. One of those mistakes is the dilemma you have provided us today with this question. It’s very common for Commanders/CSMs to express the notion of past evaluation requirements for things including, but not limited to: In-briefs, TOE placement, unit rating scheme, etc.. you get the point. However, it’s so important for you as the provider of personnel services and records management for the Soldiers in your unit, to safeguard their privacy and keep the integrity of what we do intact. SSG John Carpenter is right in that Army Regulation 623-2, paragraph 1-12 clearly states that and pretty much sets the conditions. You can also find quite a bit of info regarding this privacy in Army Regulation 600-8-104, but the simple fact is that these regulations aren’t needed to express this privacy and or needed to produce some sort of proof for your chain of command. Here’s the skinny, you, even as the HR NCOIC (an assumption based on the question) can’t even access that information. Furthermore, your brigade, your division, or even Corps level do NOT have access to view and or pull individual evaluations for anyone outside of themselves. The only way this is possible is by being granted access from the OMPF custodian from HRC (Commanding General, PERSCOM) and or the expressed consent drafted, signed and forwarded to the OMPF custodian from the individual you need access for. So, with all that being said, all you have to tell your chain of command is this, if you were authorized to view or pull this document you would be, but you are not.