I think they likely have in-house or external testing, but nothing we are made aware of. Having published figures and data greatly diminishes uncertainty, as the consumer would know that, as far as anyone knows, the batches that have been released were sampled/tested and found to be within spec.
A notion that underscores why I think this is worth considering is this: the Rockwell scale is exponential, and not linear, the functional difference between, say, HRC 57 and 60 is more notable than the values alone would imply.
If 60-62 HRC is advertised by a company, but the knives consistently come back testing between 57-59, the company currently does not publish the data, alter production, or modify the advertised values - likely because the people doing the heat treatment found it fell within their acceptable range for that steel and might not have felt it necessary to send that information to the manufacturer.
That kind of disconnect between the advertised range/value and the typical target range for the steel seems to be common, looking at the spreadsheet. The majority of the knives fell within industry specifications for the steel, but really quite a few of those were below the advertised specs.
I suppose that, realistically, the net effect of this would just be revised and more accurate advertised ranges.