Hi Joel
This is a strange one. I am sure you have already checked with OSS but just in case, I have found two OSS notes although they are either old or about an issue caused by takeover/handover:
1133810 - ToHo: Counter reading smaller than in previous document
848399 - Measurement docs: Problems after you implement Note 806624
Has there been any counter replacements before? (There is a specific process for counter replacements: Representing Counter Replacement - Customer Service (CS) - SAP Library )
Although I am not able to logically come to a conclusion on how and why counter replacements could cause such an issue. Might be someone who prepares the excel spreadsheet converted the differences into total counter readings and if the new replaced counter had already higher readings then the previous one...
Strange... Please update the thread if you find a solution for the benefit of everyone who might have the same issue in the future.
Cheers
Savas