Chapter 17 Carry back relief

I am studying carry back relief of trading losses on page 150 of the textbook, it said “partial claims, for example to leave sufficient profit to cover the qualifying charitable donation, are not allowed. These claims may therefore result in no tax relief being achieved for the qualifying charitable donations.”

However, in example 1, the answer did partially claim to leave a sufficient amount for QCD in order not to waste the relief. The answer and definition seem conflict and I am struggling right now.