Persistent ASN Lookup Discrepancy: Why Are Some ISP Identifications Inaccurate for 'What is My ISP?' Tool?

I'm currently developing a web tool, 'What is My ISP? - Find Your Internet Service Provider', which critically depends on precise ISP identification for its core functionality. Our current setup aggregates data from multiple authoritative sources, including MaxMind GeoIP, IPinfo, and direct Regional Internet Registry (RIR) data, to achieve robust IP-to-ASN mapping. We also meticulously perform ASN lookup for verification purposes, aiming for comprehensive coverage and accuracy.

Despite this multi-layered data aggregation and verification strategy, we're consistently encountering discrepancies where the tool struggles to precisely identify the actual last-mile ISP. Instead, it frequently reports the upstream transit provider or a generic 'unknown' for specific IP ranges. This issue is particularly prevalent for smaller ISPs or users operating behind larger enterprise networks. The ASN lookup process, while generally effective, sometimes returns the transit provider's ASN rather than the actual end-user's ISP, leading to inaccurate results.

This leads to several specific challenges:

• How can we better correlate IP-to-ASN data with actual ISP names, especially when the returned ASN belongs to a larger transit entity rather than the direct service provider?
• What are effective strategies for handling private ASNs or complex corporate network setups that inherently obscure the true underlying ISP?
• What are the best practices for weighting different data sources to effectively resolve conflicting ASN lookup results, ensuring the most accurate ISP identification?

I'm actively seeking advanced techniques, methodologies, or insights into common pitfalls in ISP identification and resolving these persistent ASN lookup inaccuracies. Has anyone in the community successfully implemented a highly reliable and granular system for this specific challenge?