FR Notes Depreciation page 28

First of all, thank you for this amazing resource. I am not being flippant when I say you deserve MBEs for its creation. My question is about the "Illustration - Revaluation and annual excess depreciation transfers" on page 28. I just can't work out how the historic depreciation is 5 years... I would have calculated it as 21 years left (4 years historic) to depreciate when doing the 31/12/24 statements. If the buildings/land were bought on 1 Jan 2020 and revalued 1 Jan 2024. Am I missing something? Thank you!