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?

  • $\begingroup$ Was each individual design change so slight that it didn't affect compatibility with the parts that were most recently produced but over time the changes added up? $\endgroup$
    – hazzey
    Commented Feb 27, 2015 at 20:43
  • $\begingroup$ @hazzey No. That at least would be forgivable. $\endgroup$ Commented Feb 27, 2015 at 22:05

3 Answers 3


I don't think there is any formal standard way out of this mess.

The good news is that at least tracked the changes by serial number. Inventing different models after fact seems pointless because the customers won't know what models they have. From the customer view, these are all one model but vary by serial number. Document it that way.

You could create a different manual for different serial number ranges if the changes are large, or have occasional sections in the manual that only apply to particular serial number ranges.

Make sure that the customer can easily find the serial number of units they have. This should be spelled out very clearly right in the beginning of the manual. It should warn customers that there are significant variations between serial numbers, and how exactly to identify the serial number of their unit, and then consistently use that throughout the manual when differences have to be noted.

It might be a good idea to put a chart in the front of the manual that briefly shows which features are present in which serial number ranges. You could possibly then also name each variant, like A, B, etc, then refer to that in the rest of the manual. You might even suggest to customers that they circle the variant they have, or leave a big obvious place to write their variant letter inside the front cover so they can flip back to it easily when confronted with sections that differ by variant.

  • 1
    $\begingroup$ I wouldn't be surprised if the serial numbering was up the spout as well if there's no versioning on the part numbers (e.g. pre-printed serial stickers picked in random order). $\endgroup$
    – Chris H
    Commented Feb 28, 2015 at 14:04

Tracking the various product versions by serial number is a good idea, but be careful to standardize that as well. Years ago while working for an electronics manufacturer in service and repair, I discovered two units; one was serial number 0024, the other was 00024. They had changed from a four-digit number to a five-digit one and in the process created a duplicate (except for the number of leading zeros). To avoid confusion in the future we relabeled the four-digit one to be 0024A instead. Not the best answer perhaps, but it worked. You may need to do something similar. The suggestion to document the various versions in one document with subsections and notes is a good one, if done properly.


The formal way to avoid such situation is called configuration management. Even with such a formal process there are occasions that engineering run into such scenarios. One of the most recent is the Takata Air Bag Recall. Therefore there are plenty of examples to handle such scenarios, but one size doesn't fit all.

Following are few suggestions to address the current issue as well a avoid future situations:

  1. Your customer is king, so track down and document all the customers that are affected.
  2. Fix the design using sound engineering practices. Revise all engineering and other documentation to reflect the change.
  3. Notify all customers of the situation and intended corrective action.
  4. Develop and plan to recall defective material and replace the material with revised design. Automotive and Medical industry frequently have recalls. This might be a good place to start researching for ideas.
  5. Be proactive as oppose to be reactive. Depending on the industry and customer base the possibility of any liability and litigation need to be considered.
  6. Implement a good configuration management system. This system should capture engineering change requests, implement changes and notify changes to customers (ECN - Engineering change notification)
  7. If not in place consider instituting a some type quality systems.



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