By sheer fluke on wednesday I discovered that 1Z34AB7890 is a generic fake serial number despite a warranty check showing it as real.
The XML data is showing correctly, but even now that I've changed the serial to the correct one on the front of the enclosure it's still showing in SIM as 'c7000cen_serial' while the other one is just showing as c7000trs.
I'm baffled.
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