Despite of a loyalty card being registered or not, it's alway possible to request the balance of a loyalty card. There is a webservice GetLoyaltyCardTransactions which returns all individual loyalty card transactions, both withdrawals as savings. Also, the GetLoyaltyCards webservice has properties to display the total remaining points or value balance.

It's strongly advised to display this information only to users which can identify themself by submitting both the loyaltycard checksum (for example a zipcode) and the loyaltycard number.