Help diagnosing segment membership that differs between a list-only condition and a combined segment

I'm trying to understand an unexpected difference in segment membership. I'm using test segments only; the router flow remains in Draft and has not been activated.

The intended DACH router uses these conditions, all joined with AND:
- Country is Switzerland, Germany, or Austria
- Person is in the English welcome list
- Person is not in the German welcome list
- Received Email is zero times over all time where Campaign Name equals the English Archive 01 campaign
- Received Email is zero times over all time where Campaign Name equals the German Archive 01 campaign

Observed results:
- The router segment shows 12 members, including profiles that appear to meet one or more of the exclusion conditions.
- A list-only isolation segment with just "Person is not in the German welcome list" shows 20 members and correctly excludes Profile A, who is in that list.
- A receipt-only isolation segment using the English Archive 01 campaign condition shows 21 members. Profiles A, C, and D, who have recorded English Archive 01 receipts, still appear in it.
- A separate three-condition test (DACH country AND in English list AND not in German list) shows 21 members, including Profile A and profiles outside the DACH countries.
- The saved three-condition test shows AND between all three conditions. Its membership remained 21 on a later recheck.

For context, the anonymized receipt checks show Profile A received English Archive 01 on Sep 10 and is also in the German welcome list; Profile B received German Archive 01 on Aug 24; Profile C received English Archive 01 on Sep 28; and Profile D received English Archive 01 on Sep 30. The same campaign label appears to match in flow filters for a receipt, while the corresponding segment receipt conditions do not exclude the checked profiles.

Could someone help diagnose what might explain this difference? In particular, is "Campaign" in the segment builder the same property as "Campaign Name" on a Received Email event, and are there known evaluation or refresh considerations when combining list membership, country, and event conditions?

I'm looking for a way to verify the saved event-property match and segment evaluation, not to assume there is a product defect.