So to recap, the suggestion is:
For non-claimed pending members who expire after 14 days without being approved and get auto-removed from the pending members queue:
A. Change the reason text in their record entry in the past member list from "Removed" to "Expired"
B. Add an activity log entry which indicates their removal/rejection from the pending queue due the 14-day expiration and not being approved during that time frame. Maybe "Pending member abc@... was automatically rejected/declined due to pending membership time limit expiration, via system" or something along these lines.
Part B would necessitate a new category added though, "Expired pending membership", "Pending member expired", or something like that, as the only existing category it could possibly go under would be "Rejected Member" but then it wouldn't quite jive with "Expired" in A above.