But surely, with something like ... Russian history, there's only so many questions you can ask. So, the questions are going to be inherently similar I er 6-8 years, so they can only mark on a fact'a and gen the pupils ability to discuss the finer points etc. it's subjective. If loads of kids have convincing arguments, they are going to do well. I should hazard a guess that the boundaries are higher and less variable than something like maths, a purely objective subject. So, with multiple papers, you have e more material to practice with, so they try to make it not easy. But they can make mistakes. Also, you might have a generally bright cohort or whatever.
It's not that easy to make a quiz the same difficulty.
Try and write a 5 question quiz on ... Ghosts UK tv series, then make another exactly the same difficulty, without using any repeated questions. So that's 2 papers for this year's Ghosts UK GCSE.
OK, it's a year later, now you need to make another set of 5 question quizzes, please make sure they're the same difficulty as the ones you set a year ago, now that teachers and students have had another year to deliver, interpret the source material and have also studied all your past questions in detail.
You'll probably find it's really hard to do! (And that's just a flippant example obviously, but you get the idea)