Hey he probably is only used to Swap Coolers
where I come from its 65/65
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Probably the three people who actually read their owner’s manual,lol. 
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Two different things. When any oil gets to a certain temperature it begins to thicken (sludging). Different temps for different oil types and viscosities. Take vegetable oil from your kitchen, put some in a cup then into the freezer for a few hours, then compare it to stuff that has been sitting on the counter.
In an A/C unit the refrigerant contains lubricating oil which if pushed through the system when it is too thick can cause damage to the system’s internal parts. “Migration” happens before “Sludging”
Taking the HVAC course should help…But keep in mind these courses don’t cover everything.
Different manufactures will have different “testing protocols” so doing a quick google search while on site could help as well. The industry standard of 55/65 or whatever 
is for liability as well. You don’t want to get blamed for jacking up somebody’s A/C unit. Especially in NM …
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You will end up just taking the different viewpoints and picking what ‘sounds right’ to you. There is no right or wrong (officially). Part of the challenge of home inspection is we live in the gray area where we “don’t inspect to code”, but also are rarely given a specific reason why we should or shouldn’t do something a certain way without the caveat… “well, code is…” So there’s that. I have yet to talk to an HVAC person who doesn’t snicker a little when I ask the “how cold is too cold” question. I have a heat pump on a house in Virginia… so the outside unit runs even in the winter. The HVAC guy told me… Your outside unit runs all winter, the only difference between when it runs in the summer and winter, is the direction of the refrigerant flow. So when is cold too cold…? Many (non heat pump) units have a limit switch so they won’t run when it’s below a certain temperature. But if it is close to that temperature, how do you know if it is the switch keeping the unit from running, or is it non-operational? So, again, you’ll need to pick an operating test range and stick to it. Being consistent (should a claim arise) is as or more important than the temperature threshold you choose. Welcome, and this won’t be the first ‘non-answer’ you will get to a question… as there often is no “one right answer”. Lots of opinions though.
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That many!?
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I’m a New Mexico Inspector also. INterNachi CMI, CPI and ICA Certified. The answer is you should not run a/c below 60 or 65 degrees F. Doing so can damage equipment.