I had a mortage with my credit union and at forst they were using the date the check was recieved to calculate the account. If one month I payed on the 20th more of the payment went to the principle and less to interest. If the next month I paid on the 30th then because there was 40 days there would more interest than payment.
After a few years they asked me to come in because there was a problem with my account and they wanted a face to face. According to the manager what they had been doing was agianst banking laws. What they should have been doing was calculate the monthly interest based on daily interest 28, 30, or 31 days. Add the interest to the ballance, then substract any payment. These calculations should have been done on the 1st.
If your payment is in the grase period then it is subtracted from the ballance when recieved. After the grace period late payment and payment is due. If you pay any less than the amount due you are behind in your payments. So on the next 1st interest is added again to the balance any payment recieved are substracted. If the total amount due is not paid you loan is still behind.
As far as the “advancing the due sate”. Your loan is current or behind that is all.