First off, circuit breakers can only be UL Listed by testing them IN the panels they are designed to go with, which ultimately boils down to the same mfr. But years ago, mfrs started designing panels for residential use where the mounting and connections were virtually the same. We used to collectively refer to this type of breaker as "interchangeable"; you could plug a Bryant breaker into a Murray panel or a GE breaker into a Sylvania panel, as long as they were the same style of breaker. But some time in the 80s, a lot of field failures took place and in ensuing investigations it became clear that unless specifically tested, these mfr mismatches did not always perform as expected, then created a conflict in determining who's fault that was, the panel mfr, the breaker mfr or the person who did it.
Since the lawyers only wanted to go after deep pockets, and it was unclear which mfr had the issue, a lot of homeowners insurance companies ended up holding the bag. That then prompted them to get UL involved, who came up with a new process by which otherwise UL listed breakers could also be "classified" to be used in some specific panels, so long as the BREAKER mfr tested them in those specific panels and listed those specific panels in their installation instructions. This system by the way NEVER includes "series ratings" for higher AICs, so if you are in an area that requires 22kAIC or higher, Classified Breakers are immediately eliminated as a possibility.
So technically, if the specific panel that you are looking at is on the specific list of tested panels in the Classification certification of those Homeline breakers and 10kAIC is acceptable in your area, they are perfectly legal. If not, they are illegal. That level of detail is virtually ignored in the retail industry, because if a homeowner installs something themselves, they assume their own risks. Electrical Contractors however cannot ignore the liability associated with willy-nilly use of Classified breakers, just as we cannot ignore any other portion of the NEC, and the misuse of a Classified breaker would violate 110.3 no matter what.
So now we come up against the kind of situation you are involved in; YOU did not originally install them, but now YOU have seen them, so does that then shift responsibility for investigating whether they are appropriately applied over to you? Good question. The SAFE BET, as others have said, is to just replace them, because the time and hassle to investigate them is worth more than the breakers themselves in most cases. But with smart phone access now, it might only take a minute or two to find and download the list of approved panels for Homeline breakers to find out. So that makes it a judgement call.
Of course if you are in an area that requires more than 10kAIC, you don't need to bother checking, it's an automatic fail.
