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My internal alarm bells started going off as soon as I read about datum AA and datum M. Shouldn't it be possible if not standard practice for the design software to issue a giant warning if you have a part that is defined by two datums that are almost but not quite the same? If they aren't the exact same datum then something like this will inevitably happen.

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There is nothing wrong with 2 datums, the issue is that during machining this is not "a part" but an assembly that moves. There are so many failings from my POV in the manufacturing process and verification of the part, which is summarized nicely by the following quote:

. Furthermore, initial inspections at the start of the production run were supposed to verify that the manufacturing process was creating products that satisfied the “design intent,” but the initial products were checked against the manufacturing drawings, not the design drawings.

It’s definitely possible, but the checking system was probably built under the implicit assumption that the sources of truth for the checks (datums, dimensions) were correct.

2 datums might need to be very similar but not quite the same, so checking for it might present a lot of hard to handle false positives and make the system very complex.

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