Recipients beyond the number of values in the pool will not receive a code. Load a pool at least as large as the audience and check the remaining count before a large campaign.
A value is bound to its recipient when it is issued, so a repeated message to the same person reuses their value instead of spending a new one.
Yes. Put the same variable into the fallback text and the recipient sees an identical code in Viber, SMS or push.
A CSV file with one value per line, or manual entry directly in the panel.
Yes. Every value in the pool carries its status and the time it was issued, which you can reconcile against redemptions in your own system.