A replacement date is only useful if somebody sees it in time to act. Most suppliers have the data and no mechanism, so the date passes unnoticed and the next contact is a failure call.
Start with what actually sets the date
There is rarely one clean number. Depending on the item, the replacement date comes from one of four places, and knowing which one applies changes how you track it.
Manufacturer service life. Some components carry a stated life from date of manufacture regardless of use. Rubber compounds age whether the assembly is in service or sitting on a shelf, which is why shelf time counts against it.
Test or certification interval. Where an item is periodically proof tested or recertified, the clock runs from the last test rather than from installation. Miss it and the item is out of service on paperwork alone, whatever its condition.
Duty cycle. Hours, cycles, or throughput. Far more accurate than calendar time and far harder to capture, because it needs data from the equipment rather than from you.
Condition. The item is replaced when inspection says so. This is the most honest basis and the least plannable.
In practice most distributors run calendar dates with condition as an override, because it is the only version that works without integrating into the customer's control system.
Why dates get missed
The date lives in the wrong place. On your side it sits in an order history nobody opens. On their side it sits in a spreadsheet the person who built it no longer maintains.
Nothing connects the date to the object. The record says a hose assembly is due. Nobody can identify which of the sixty on that line it is without crawling the plant.
The alert has no owner. An email to a shared inbox is not an owner. Somebody has to be responsible, by name.
Lead time is not in the calculation. An alert on the due date is already late. If the item takes eleven days to build and ship, the alert has to fire at least that far ahead plus scheduling slack.
Building something that holds
Four things, in order.
Tag the item at the point of manufacture or supply. Not on receipt, not at installation. If the tag goes on when the assembly is built, the record carries the manufacture date, the specification and the test certificate from the beginning, and none of it has to be reconstructed later.
Set the clock from the right event. Manufacture date for age-limited items, last test date for certified ones, install date for duty-based ones. Storing all three costs nothing and saves an argument.
Alert on lead time, not on the date. Work backwards: build time, transit, the customer's own scheduling window, and a buffer. For most industrial consumables that lands somewhere between three and six weeks ahead.
Make the next action one tap. The alert should carry a reorder for the exact specification of the item being replaced. If it makes somebody look up a part number, the urgency dissipates and the order goes elsewhere.
Handle shelf stock deliberately
An item that has sat in your warehouse for eight months arrives with eight months already spent, if its life runs from manufacture. Shipping it as new is a real problem, and it surfaces at the worst possible moment when somebody reads the date on the tag.
Track manufacture date on stock, ship oldest first, and be upfront about remaining life on anything that has been sitting. Customers respect it and it prevents the conversation where they work out the arithmetic themselves.
The measurement that tells you it is working
Not how many alerts fired. Count what proportion of replacements were planned rather than reactive.
If that number is not moving after two quarters, the alerts are firing into a void. Usually the fix is not more alerts. It is that nobody with authority to act is receiving them.