Numbers are numbers, and yes, they will vary based on the lab and the lab equipment used.
Speaking from vet med... in chronic disease states, there might be a particular lab value or set of values that we are looking at when we run repeat bloodwork every so many months. We are looking at trends. We are looking at whether or not that number is good for that animal with that disease state.
We have no hidden agenda of hiding the truth from our patients. In fact, we might say something like, "Well, the XYZ lab value is still elevated above the range of most normal animals, but this is actually a very good number for a patient with this disease. Here's what we might do if you want to try to make it better, but realistically..."
Given that I was just diagnosed with 'the big D' a few weeks ago, I realize I haven't had near the personal experiences that almost all of you have had with this disease..
But I think it's important to remember that your doctors are probably not trying to hurt you, and that they realize some of these numbers may be the best that someone may be able to get with the big D. And if you have concerns that they are hiding things from you or that you aren't getting the whole story, just ask. Really. Don't be afraid to ask if it's possible to have an A1C of 5.whatever... and ask how many non diabetics actually have a 5.whatever A1C.
Also, just as an aside.. there is currently research going on with A1C and figuring out whether it's actually as valid as everyone thinks it is in people... In animals, we measure fructosamine.. and there is some suggestion that measuring fructosamine in people may provide a superior snapshot as compared to A1C (one of my docs told me this, but I haven't looked for any of the papers on it. Just food for thought.)
There's a reason why they call it 'practicing medicine'... 'cause it ain't ever gonna be perfect, there's too many variables! And things change ALL the time.