Hi John, its probably because RTI submits year to date figures so provided the alterations have been done, you need not make a special submission for amended figures.
Having said that, yes I would do sick pay or any amendments in the correct pay period.
PS
Here's a list of RTI error messages should anyone encounter them.
I have just changed payroll software to Moneysoft and may have mucked something up on RTI.
An employee was off sick from 19th August- 30th August. There was no pay for the two weeks previous (additional leave no holiday pay) I entered the sick pay details in week 21 and a calendar popped up for me to put the dates in. I then noticed the sick pay had gone into week 20 and 21, not 21 and 22. Not to worry I thought, it doesn't affect anything so then I submitted the RTI for week 20 and it just listed it as basic pay. Week 21 listed it as sick pay £121.38 with £86.70 paid. I had already submitted week 20 but didnt submit week 21
I phoned Moneysoft and apparently I should have done an adjustment to pay sick pay in the right pay weeks, as sick pay becomes due the same week they are off sick. I have done this and now week 21 looks correct on RTI but I am concerned that HMRC will think the employee received £34.68 on week 20, when he didn't. The guy at Moneysoft said RTI will correct itself but I don't see how.