Not certain, but its possible you're running into a known issue, which you can find more about on this thread: https://www.jamf.com/jamf-nation/feature-requests/4389/model-name-not-always-correct
Short story is that the JSS determines the full human readable computer name by using a translation between the model identifier and the full model name that is hardcoded into the JSS. The issue comes in because Apple has for a number of years now been re-using model identifiers. For example, an iMac released in Mid 2015 and a revision to that Mac released in Mid 2016 may end up using the same model identifiers, even though the full names we see for each one may be different. So when the JSS encounters one of these duplicate model ids, it only knows of one full model name associated with that model identifier. And often its the wrong one. And that's what you see in the JSS.
On the thread above and on a few others are EAs that can help pull the actual full model name from Apple, so its going to be more accurate.
Again, I don't know if that's the exact issue you're seeing or not, but it may be.
