Did anyone call them by their numbers back in the day? I grew up the child of an IBMer and only recall hearing "PC", "XT", "AT". There were some big IBM machines and displays that would be referred to by numbers ("3090", "8514") but I never heard that for the PC system units.
5150 I occasionally heard (though something like “original PC” was more common) to disambiguate reference to the specific model from the general class once the XT, AT, PCjr, etc., made the term ambiguous even when prefixed with “IBM”; don't recall the other model numbers for system units being used.
I was about to be like "surely you mean the S/390 series" but nope, you are correct! Apparently 3090 came in between the S/370 and S/390 series: https://en.wikipedia.org/wiki/IBM_3090
https://history-computer.com/ibm-pc-5150-guide/