I was working for Meta in Bellevue, WA in 2022. Got laid off. Applied to several positions at MS (I was living in Redmond at the time), couldn't get a callback. Months and months go by, get a job, move across the country, get an email 9-12 months after applying that they'd like to interview me. I didn't even bother responding.

That's where the ghosting comes in. If you're always ghosting, then you always have recent people to get back to, not months old.

The pipeline isn't a lossless FIFO queue, in other words. People go in one end and are dropped out the other. In between are the recents you can call if a spot actually opens up.

Exactly, you don't build up a catalogue of people you can get back to.

Ie. this technique does not make sense - search for people on demand instead.

Searching for people from scratch in reaction to a sudden demand will have much more latency than having someone you can pull from a recent roster of validated candidates.

It's exactly the same like how an integrated circuit can pull a sudden power demand from a capacitor placed next to it (often required by the datasheet), rather than from the power supply upstream, so there is no voltage sag affecting it and nearby components.

Or, in computing, prefetch and speculative execution, and such.

If you have a "sudden demand" demand I would say that you have other issues in your HR planning strategy.

You should not plan to do projects that require you to hire a special resource tomorrow.

And also: Having an open pipeline really does not hedge for that, and you open pipeline might not align with your sudden need.

It can take months to hire a specialist from both but if you're constantly spinning plates, you have some lukewarm contacts as well as a list of obvious no's.