Some people still sign in with the four digits typed into the Time Clock spreadsheet. Slab no longer accepts that spreadsheet as a sign-in, so those people are locked out until Slab has a PIN of its own for them. Migrating copies those same four digits into Slab so nobody is stranded — it does not make the PIN secret, because the spreadsheet still has it. Everyone migrated stays on the queue above until you reset them.

Every person Slab will let sign in — the Time Clock roster and the people added in Slab, in one list. Where their PIN lives is the column that matters: a PIN only its owner has ever seen, a PIN copied from the spreadsheet, or no Slab PIN at all.