pg_basebackup vs archive_command - looking for WAL archive older than archive_command start

I turned on archive_command and have wal archiving going.

I did a pg_basebackup and copied the resulting file from source machine
to target, yet when I restore I am getting

requested WAL segment 00000005000008AE0000009B has already been removed

The earliest WAL archives I have are

00000005000008D20000005C.00000028.backup.gz
00000005000008D20000005C.gz
00000005000008D20000005D.gz

Why is the pg_basebackup restore looking for a WAL file that is even
older than the ones I have, when I turned on WAL archiving before I
started the pg_basebackup?

Also, why is that one WAL archive named differently with .backup?

Normally I restore with pg_basebackup and streaming replication, which
works well, but lately due to constant network disconnects I have to
make the pg_basebackup in the source machine and rsync. That is why I
turned on WAL archiving before starting the base backup since it would
take some time to copy the base backup file over.

The command I am using to create the base backup is
pg_basebackup  -U UserName -h 127.0.0.1 -D - -P -Ft | gzip >
Basebackup.tar.gz

Any suggestions?