First four years special relief

Q13 MAX, page #329 , the loss relief for 2021/22 is given against 18/19, 19/20 and 20/21

Why isn’t it 19/20, 20/21 and 21/22 , don’t we use total income of current tax year?

Page #238 answer to eg 5

Loss relief for 2020/21 is seta against 18/19, 19/20, and 20/21 ?
Which is the correct one? Do we include current year tot income? Or the prev 3 years?

Special loss relief arising in first 4 tax years

Suppose trading started on tax year 2018
Relief is given only for 2018,19,20 and 21 ?
Loss in 21/22 set against 18/19,19/20,20/21

Loss in 20/21 set against 19/20, 20/21

Is it like that? The rule is loss carried back three tax years, but we have applied it differently in both questions.. I didn’t understand..