A lead time is not a delivery date. It is a statement about a manufacturing queue, and the number quoted depends heavily on who is quoting it and why.
Stock shown at a distributor is real but shallow — it can vanish in a single order from someone larger. A factory lead time reflects the queue at the manufacturer and moves when demand shifts. A quoted date that never changes across several enquiries usually means nobody has re-asked the factory. And a long lead time on a mature part sometimes means it is being quietly de-prioritised rather than genuinely queued, which is a different problem: the next revision may be a discontinuation notice.
The signals worth watching are cheap to check. Compare the same part across several distributors; wide disagreement means nobody really knows. Look at whether the manufacturer still lists it as recommended for new designs. Check whether the package and temperature grade you chose is the volume variant or a niche one — the unusual option often carries the long queue while the standard part ships from stock.
The design-stage response is boring and effective. Pick parts that are recommended for new designs, prefer packages and grades that ship in volume, and identify a genuine alternate for anything that would stop a build. Doing that costs an afternoon during schematic capture. Doing it after a shortage costs a respin.