intermittent ISP detection failures with specific IPv6 ranges causing `unknown` responses

Hey everyone, running into a bit of a wall with our "What is My ISP?" tool, specifically around ISP detection accuracy.

We're seeing intermittent failures where some IPv6 addresses, particularly within certain delegated ranges, are consistently returning 'UNKNOWN' or 'N/A' for their Internet Service Provider. our current backend logic for ISP detection relies on a multi-stage IP lookup: first, a reverse DNS query, then cross-referencing with regional internet registry (RIR) WHOIS data (ARIN, RIPE, APNIC, etc.), and finally, our internal ASN database. for most IPv4 and many IPv6, it's solid. but there are these specific IPv6 blocks...

here's a simplified example of what we're seeing in our logs:

[2024-07-26 14:35:01] INFO: Processing IP: 2001:db8:1234::/48
[2024-07-26 14:35:01] DEBUG: rDNS lookup failed for 2001:db8:1234::1
[2024-07-26 14:35:02] DEBUG: WHOIS query on 2001:db8:1234::/48 returned 'UNKNOWN' for org-name
[2024-07-26 14:35:02] ERROR: ISP detection result for 2001:db8:1234::1: UNKNOWN_ISP

we've checked the RIR databases manually, and while some delegated prefixes show the LIR, the actual ISP name or AS info isn't always readily apparent or consistently structured. any advanced strategies or alternative data sources you guys use for robust IPv6 ISP detection, especially for these tricky delegated blocks where WHOIS is less informative? trying to get this more reliable for our users.

waiting for an expert reply!