I think it’s highly unlikely they’d give you mocks at home to complete and use that to help you determine your grade. It’s quite easy to just look up mark schemes for past papers and get high marks on papers while still making it look like your own work, especially since it’d be online, there’d be no regulation whatsoever. You shouldn’t stress about it because what’s done is done and your grades will most likely be determined from past mocks and past exams in class, (also they mention “past attainment” based on the copious amount of data exam boards have on you, in which case i think they’re talking about GCSE’s?)