The device identifier (DI) identifies the make and model; the production identifier (PI) identifies the specific lot, batch, serial number, or expiration date.
21 CFR 830.3
What people get wrong
A UDI is the DI and PI concatenated together. The DI alone is what gets submitted to GUDID as the catalog record for a device model; the PI is what changes unit to unit or lot to lot and is what actually lets you trace a specific recalled batch. A device with variable production characteristics (like an expiration date) is required to carry a PI on the label even if the DI alone would technically identify the model.
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