I'd argue that the archival happens the moment the DRM is stripped, the seeders are just helping out with the data replication part - but I get what you're saying.
As an aside, HDCP is broken in practice but frowned upon for archival, since it requires a re-encode, introducing generation loss.
No, HDCP itself is broken. According to the DMCA, and corresponding legal precedent[1], you're allowed to convert one version of HDCP to another. You can buy legitimate adapters off the shelf (provisioned with valid keys) to convert HDCP 2.2 to HDCP 1.4. No jumping through hoops, no legal grey areas (for now), it just works.
HDCP 1.4 uses export-grade (broken) cryptography, the master keys are available on the public web. But you don't need to bother understanding the specifics, since just about any HDMI 1.4 sink you buy from China (whether it's a capture card or splitter) will strip HDCP 1.4 as a matter of course.
You may be allowed, but how would such a device get keys from DCP, and how do they avoid all of those keys being immediately blacklisted from being used for HDCP downgrades? HDCP 2.2 isn't the latest version either.
They don't get blacklisted because what they're doing is explicitly allowed, and very widespread. Yes, HDCP 2.3 is the latest version but HDCP 2.2 is all you need in practice. I can't talk from experience on 2.3, but I can on 2.2, so that's what I referenced.
If you don't believe me but also don't want to buy any hardware to test for yourself, search for "HDCP 2.2 splitter" on amazon and read the reviews (but beware of confused customers who aren't aware of the difference between HDCP 2.2 and 1.4).
I'm not sure precisely why it works, but I can tell you for sure that my upstream devices cannot tell, and that it works in practice. I assume the splitter only tells the source about one of its downstream sinks (if at all), but not both. (maybe that makes it non-compliant and at risk of revocation - I'm not sure, but do know that it hasn't happened yet)
As an aside, HDCP is broken in practice but frowned upon for archival, since it requires a re-encode, introducing generation loss.