The article discusses the problem of the formation of unclaimed material reserves in industrial enterprises with a long production cycle. In the context of design-oriented production, the calculation of the need for materials in the early stages is preliminary and is clarified as the documentation is being adjusted, which leads to discrepancies between planned and actual consumption, as well as the accumulation of excess inventory. The aim of the study is to assess the potential lack of demand for material resources and to justify the maximum share of their primary purchase under project uncertainty. The relevance is due to the high proportion of materials in costs, the growth of unclaimed stocks and the limited applicability of regulatory methods in the early stages of procurement procedures. The empirical database includes data on inventory balances, a history of adjustments to procurement standards, and an archive of material replacement maps. The work uses the calculation of savings from replacement, the coefficient of relative substitutability, an assessment of the volatility of norms and the coefficient of material involvement in production. Partial estimates for each of these indicators are combined into an integral score of the potential lack of demand. On this basis, a classification of production stocks is proposed, dividing materials into three risk categories. For low risk (5–6 points), the recommended share of primary purchase is up to 100%, for medium (3–4 points) — up to 85%, for high (0–2 points) — up to 70%, or a delay in purchase. The proposed classification algorithm has been tested on the data of an industrial enterprise with a long production cycle. The developed classification reduces the flow of unclaimed stocks without stopping the production process.