I am now in charge of a product line my company has been shipping for a decade. One of the previous product engineers was... shall we say, less than conscientious about sustainability and proper documentation. We have shipped hundreds of units, of multiple design variants, under the exact same part number. The manual presently reflects only one variant, meaning many users can't use it. And we've had multiple instances where a user has tried to reorder a unit by part number, only to find that what we ship them does not match what they already had.
Obviously, this is terrible. One does not change the specs or user interface of a product without also changing the part number. We will avoid such things in the future. But my question is about the past.
We have, on paper, documentation indicating what design variant each serial number corresponds to. My thinking is to create a spreadsheet, and name each variant retroactively, so we can at least support users that call in or place reorders. We would then create proper manual(s) so that the user can, based on their serial number, understand the operation of the units they have.
But I'm just making up that solution. It occurs to me that there may be formal, industry-standard methods of dealing with such things. Is there a procedurally-correct way to handle my existing install base?