gyb with --service-account not restoring all messages

Restoring from multiple exported MBOX files using --service-account into a single empty mailbox for review.

Expected quantity is 195 messages. The message count in the target mailbox increased from zero to only 95. This number happens to be the same as the first two MBOX added together.

Looking at a metadata spreadsheet, none of the message Id are duplicate. Ran the restore 2x in a different order to make sure it wasn't hitting a velocity problem or other error that I didn't see. No error messages.

Using gyb-1.81-windows.

Sanitized CLI:
`> gyb --email aggregate@domain[.]tld --action restore-mbox --local-folder "C:\exports\user1@domain[.]tld" --service-account`
`Restoring from 11.11mb file`
`C:\exports\user1@domain[.]tld\qry_export-MBOX--user1@domain[.]tld-ZzzzZ1.mbox...`
`restoring 1 messages (50) - 100.00%`
`done!`
`> gyb --email aggregate@domain[.]tld --action restore-mbox --local-folder "C:\exports\user2@domain[.]tld" --service-account`
`Restoring from 22.22mb file`
`C:\exports\user2@domain[.]tld\qry_export-MBOX--user2@domain[.]tld-YyyyY2.mbox...`
`restoring 1 messages (45) - 100.00%`
`done!`
`> gyb --email aggregate@domain[.]tld --action restore-mbox --local-folder "C:\exports\user3@domain[.]tld" --service-account`
`Restoring from 33.33mb file`
`C:\exports\user3@domain[.]tld\qry_export-MBOX--user3@domain[.]tld-XxxxX3.mbox...`
`restoring 1 messages (11) - 100.00%`
`done!`
`> gyb --email aggregate@domain[.]tld --action restore-mbox --local-folder "C:\exports\user4@domain[.]tld" --service-account`
`Restoring from 44.44mb file`
`C:\exports\user4@domain[.]tld\qry_export-MBOX--user34domain[.]tld-WwwwW4.mbox...`
`restoring 1 messages (89) - 100.00%`
`done!`

Start by reproducing the four restore-mbox commands with --service-account and compare the cumulative mailbox count with the 195-message expectation. Trace the restore-mbox and service-account entry points to determine why later MBOX files complete without restoring all messages. Done means all 195 unique messages are restored and the command reports failures rather than silently completing.

Written by the indexing model from the issue text.