In fact you can get the original samples taken directly from the ROMs of old digital drum machines, which is maybe 60% of the character. The other 40% is a combination of the imperfect digital-to-analog converters and analog output stages of the time, the way effects like pitch shift were implemented (often by changing the sample rate, which is hard to emulate), and the control gestures idiomatic to the machine.
Legendary drum machines fall mostly in two categories : analog ones such as the Roland TR808 (and also electronic drums such as the Simmons SDS5), and early digital ones such as the LinnDrum and the Oberheim DMX, which use low bit samples (8 or 12 bits at most) and have an highly coloured sound (so that people still like to make new ROM kits for these, then sample the output).
Later models (starting in the 90s) have "CD quality sample" and probably aren't particularly worth sampling.
However some late machines such as the MPC series have audibly special sequencers, and "swing" in their own, peculiar way. So sampling individual sounds isn't particularly interesting, but sampling drum loops can be interesting.
> the MPC series have audibly special sequencers, and "swing" in their own, peculiar way.
Best explained by Roger Linn himself:
> My implementation of swing has always been very simple: I merely delay the second 16th note within each 8th note. In other words, I delay all the even-numbered 16th notes within the beat (2, 4, 6, 8, etc.)
https://www.attackmagazine.com/features/interview/roger-linn...
It's a bit more than bit depths, some use non-linear encoding (mu-law etc) which also contribute to uniqueness.
> these would be analog drum machines and the sampling is for convenient use in a digital workflow?
Convenience and also price. A real Roland TR-808 will set you back about $5,000 dollars on the used market.
Sampling a sample can definitely be useful, if the original sample is in an inconvenient format (e.g. inside some hardware). Of course, this business is in a legal gray area, because the recordings inside the machines are copyrighted. But they are resold with some "processing" that could potentially be considered transformative enough. This is niche enough that I doubt it will ever be tried in court.