A scaffold is only as good as what it is fixed to. The drawing can show a perfect tie pattern and still fail if nobody tested the substrate.
Test first, trust later
Anchors get proof-tested before the structure goes up, and a percentage get re-tested as the lifts rise. Old brick, rendered blockwork and lightweight cladding all behave differently from the concrete assumed in a generic calculation.
Where ties go missing
Usually where another trade needed the wall. A removed tie is an alteration, which means an inspection and a new tag. If a tie has to come out, it comes out with a replacement already in place.
