On the more general point, what we are re-teaching or re-covering depends on the subject.
Things like Science, History etc - what has 'gone' has gone. We are not attempting to cover the missed content.
In English, we are teaching what we usually teach in terms of texts, but at least initially there will be a stronger focus on marking for and reinforcing basic skills in punctuation etc. We have taken advantage of the fact that the timetable has had to be reformulated for staggered arrivals, breaks etc (and the lack of assembly and limits on some subjects like music) to introduce specific discrete sessions for handwriting and spelling .
In Maths, we have looked back at 'what was not taught'. Due to the way the curriculum is structured, the next time those topics are taught tends to be in the spring / summer term of this year, so the min re-planning element will come in later in the year. For the moment, we are again using a different timetable to make sure that the previous year skills that underpin current teaching are also secure - either by starting each sequence of learning in a slightly different place or through different activities or practice of e.g. number bonds, times tables etc.
I am expecting the range of performance at the start of the year to be wider than usual (though possibly not as wide as the most extreme class i have had recently, where there was a gap of around 9 years from the child working at the level of an average 4 year old to the child working comfortably at a level typical of a 13 year old), and i would also expect that to be much more related to 'experience during lockdown' than 'actual ability' and so to change quite rapidly over the course of the year. That's to be expected, and it's what we have prepared for.