To clear up some questions and misinformation:
The deadline to submit marks varies dependant on subject and exam board. Pearson GCSE Art, for example, is 48 hours before the external moderator visits. Moderation visits basically go up to the end of June, so there is plenty of time to send out raw marks.
You cannot add raw marks for component 1 and component 2 together and compare to grade boundaries, as this doesn’t account for scaling (comp 1 60%, comp 2 40%) For example, on Pearson GCSE raw marks for both components are given out of 72, giving a maximum mark of 144. The grade boundaries are out of a maximum mark of 180.
The raw marks could be moved up or down during external moderation. Grade boundaries can move too by a couple of marks or so in either direction. Students, nor teachers, are informed if this happens, they just have to figure it out on results day.
Certainly for GCSE Art, getting a lower raw mark than they received during mocks isn’t really a thing. Their mocks ware part of their final component 1 raw mark, and contribute to 60% of their grade. It is possible that they have not created work to the same standard since mocks, and work which is significantly poorer quality could affect ‘consistency’ if that wording is used in assessment objectives. However, since mocks all students will have spent most of their time developing component 2 - again if this is underdeveloped or poorer quality they may have a lower raw mark for it, then component 1. Once scaled and added this could mean overall they fall into a lower grade boundary than if their component 1 would be if it was worth 100%.
When you receive your raw marks you cannot appeal on the grounds you think it should be higher. You can only appeal the marking and internal moderation process, and you would have to show that this process has been inadequate or the assessment objectives have not been applied fairly. This is very difficult to do. You can request to see assessment marksheets which can be helpful in showing how marking has been applied. You may be able to see marksheets from over the duration of the course which might show how mark has changed over time. If you believe you do have grounds for an appeal you can ask the school to have it remarked at another school - this might not go in your favour, they could mark it lower. Believe me, no one wants to give your child more marks than their actual teachers, they will always try to award the most marks they can justify. Poor outcomes are scrutinised by leadership and reflect badly on departments, nobody is going to go out of their way to mark a student down for fun or some sort of personal grudge.
I completely agree it is a ridiculous JCQ policy that benefits no-one and causes unnecessary stress for teachers, students and parents, at an already fraught time of year.