Non-Incidental Materials and Supplies are deducted when used, not purchased.  It seems like pretty much the same timing as keeping Inventory, so is there a reason why they are using NIMS as opposed to Inventory?

But there is a third option, *IF* they qualify for it.  The simple version is that if they DON'T keep Inventory for other purposes and their Accounting Procedures deduct it for their 'books', then it can also be a tax deduction.  See Regulation §1.471-1(b)(6).

https://www.irs.gov/publications/p538#en_US_202112_publink1000270704

https://www.law.cornell.edu/cfr/text/26/1.471-1