There is a lack of consistency - although I am fully in favour of the online system.
A friend's report date was 25th October. However, he returned through Don Muang on 25th August - that meant that he did not need to report until 23 November.
The Immigration arrival system is not joined up with the online system and, sure enough, he got a reminder last week. He thought he would submit anyway and expected to get a rejection (as I did after doing the same thing).
No, Immigration approved his submission and, despite putting in the entry date of 25 July, he is now approved to 16 January.