Struggling with cross-channel attribution modeling discrepancies: why is my GA4 data not matching CRM conversions?

so, we've been really trying to fine-tune our cross-channel attribution modeling in GA4, integrating it closely with our CRM. the goal is to get a unified view of customer journeys and conversion paths, but we're hitting a wall and this is really messing with our overall conversion tracking accuracy.

we're seeing persistent and significant discrepancies between GA4 reported conversions for specific channels (e.g., organic search, display retargeting) and what our CRM registers as attributed to those same channels. the delta is often 15-20% lower in GA4, particlarly for high-value leads with longer sales cycles. it feels like a fundamental breakdown in how events are being passed or how GA4's data-driven attribution is interpreting the sequence, maybe a post-conversion event isn't being correctly associated.

when debugging, we sometimes see delayed or missing gtag('event', 'purchase', ...) calls in the console for successful CRM conversions, leading to gaps. here's a simplified console observation:

// Scenario: CRM records conversion from 'organic' 2 days ago
// GA4 DebugView for the same user ID shows:
// Timestamp: T-48h, Event: 'page_view', Source: 'google / organic'
// Timestamp: T-24h, Event: 'add_to_cart'
// Timestamp: T-0h, Event: 'form_submit' (custom event, tracked)
// ...
// MISSING: gtag('event', 'purchase', ...) or equivalent 'conversion' event for this user.
// CRM reports conversion, GA4 does not attribute it despite earlier touchpoints.

what are the most common, yet overlooked, technical gotchas when trying to align GA4's data-driven attribution modeling with CRM-recorded sales, especially concerning event deduplication or late-stage conversion tracking? are there specific server-side tagging configurations that might mitigate this data drift?