FWIW, having a human regularly count the equipment would have also uncovered the error. As well as other interesting reasons that discrepancies arise, such as theft. Always important remember that these systems are tools, not the truth, and have to be reconciled to the truth on a regular basis.
Simple counting would not uncover the error. The company was required by support contracts to have some equipment in store in case of failures to quickly replace what failed. And the error was related to not updating in one Excel sheet information that a particular long-term contract was replaced with different one requiring less equipment on storage after updating another sheet. The Access DB with the support of enforcing complex cross-table constrains detected that.
