The stability program I managed only required a periodic (quarterly) spot check to ensure the inventory systems are functioning. That spot check was proceduralized and documented as an “Internal Audit” activity which was out of scope for external audits (and even internal audits). If an auditor wanted to see that documentation, we could give them an affidavit confirming the spot check was performed, but not the actual raw documentation. That said, our spot check was a check list of several compliance and maintenance related things and a simple list of 10 studies counted for accuracy of inventory. If more than 1 item was inaccurate of if two periods in a row showed problems, an immediate full inventory was conducted of that chamber. If more than more than one chamber in two periods had inaccuracies a full inventory was conducted. We have only conducted a full inventory once in 12 years.
That said, annual chamber inventories are, in fact, not a requirement, and in my opinion, they are an area where many programs spend too many resources for very little return. An auditor is interested is accuracy of your inventory during their visit and should not be interested in the accuracy of your inventory 18 months ago during the 3-day shutdown. If you have a modern LIMS system that updates inventory automatically as samples are added or removed with each transaction verified then apart from an actual thief coming in, your inventory should remain accurate for the life of each study. Confidence in that system can save a lot of time and money.