Meta's Test Events tab is excellent for what it shows. There are three things it does not.

Blind spot 1: match quality

Confirms an event was structurally valid. Match quality scores are computed only on production events with a 24-hour delay. A test event can be perfect and still match no real user.

Verify in production: after a day, check Diagnostics > Event Match Quality. Below 5/10 is a problem.

Blind spot 2: deduplication with the Pixel

If your event_id-based dedup is misconfigured, the test passes but production double-counts.

Verify: in Events Manager, look at the dedup column. Above 80 percent overlap means dedup is working.

Blind spot 3: rate limits

Test sandbox has no rate limits. Production caps around 1000 events per second per Pixel. Spikes can hit the limit and trigger 429s, invisible from the test tool.

Verify: monitor your tagging server logs for 429 responses from Meta.

Use the test tool for structure. Run to production for 24-48 hours. Check match quality, dedup overlap, and 429 rates separately.