Why would they send out such a late report based on old data? This does not make sense.
What happens is this. The school Forward Plan or calendar is put together with an assessment point every half-term. In order to assess them you have to have taught them, so you can't do it at the start of the half-term (as they won't have learned anything, and besides, the teachers will only just have entered their last set of data and will be trying to, you know, plan some lessons. So you aim to assess in, say, week 4 of a 7 week half-term and put the marks out to parents in week 5, leaving time for queries. Sounds sensible, right? Actually, no. Firstly, three weeks of teaching in the final half-term of the year isn't very much at all. There are assemblies, trips, speaking exams, Drama performances, sports events etc. Hardly anything gets done. So the assessments happen in a rush at the end of week 4.
Now it becomes fun. Let's say Y7, 8, 9 and 10 all need to be assessed. Y10 students in core subjects need to do two papers for GCSE and, on reflection, it's decided Y9 should do that too, because it's 'good experience' for them and gives us 'a more accurate idea of their attainment'. Okay. That gives some teachers (those who teach core subjects and have, for example, a Y9 and two Y10 classes) 180 papers to mark in a week. So, to prevent teachers walking out in even greater numbers than is the case at the moment, the deadline is moved to week 6.
Deadline met. Should be sorted, yes? Um, no. Time needs to be built in to moderate the papers and make sure the grades are accurate (this isn't really what happens, because time, but a token few days are built in). Reports are now due to go out week 7.
Etc.
It is a farce. You can get predict what a student will get in their GCSE by conducting a rushed assessment, but that is exactly what this will have been.