Scotlands cruise critic

Cruised November 2023. Added $1800 worth of free onboard credit by using the $0 add ons ( $500, $300 & $100 each). Was given $1800 on our account when we boarded. Have another 2 cruises booked this year.. used the same method of adding the $0 credits to both . My account shows up as $0 for the first cruise and $1000 for the second cruise 🤷🏼‍♀️ no logic applied but im just happy to receive the “free” money .