Long before I had the tools or incentive to buy the tools or hire someone who already owned the tools (risk assessment tools), I used a "seat of the pants" judgment when trying to implement a "semi-JIT" purchase/inventory policy.
When products were "off-the-shelf" from multiple producers, I bought only the quantity I estimated I would use in the LONGEST lead time from any producer and made sure to reorder before my own shelves were bare.
When it came to custom-made products, all bets were off. Depending on product and its price, I arranged for either supplier or me to carry "safety stock" in a secure third party facility to guard against events (force majeure) which could stop our production flow.
As a supplier of custom made products, I not only arranged "safety stock" of our products (only with guaranteed blanket order from customer), but I also contracted with production equipment manufacturers and competitors to be able to get back into production with same or similar equipment if a disaster destroyed our machines. The overriding theme is "Never leave a customer holding the bag." It is important to use this in marketing AND to charge for the "security" it gives the customer. An important facet is to demonstrate the "knowledge" concerning the product is not lost if a disaster occurs.
So, in retrospect, it seems to me the TOTAL risk assessment of ever being without critical materials should be the most important aspect of JIT (just in time) inventory planning. Administrative costs of multiple ordering can be ameliorated by issuing blanket orders for estimated annual usage and releasing delivery quantities and frequencies against the blanket order (i.e. only negotiate price and contract review once per year.)