  When locally engineering F-theory models some D7-branes for the gauge group
factors are specified and matter is localized on the intersection curves of the
compact parts of the world-volumes. In this note we discuss to what extent one
can draw conclusions about F-theory models by just restricting the attention
locally to a particular seven-brane. Globally the possible D7-branes are not
independent from each other and the (compact part of the) D7-brane can have
unavoidable intrinsic singularities. Many special intersecting loci which were
not chosen by hand occur inevitably, notably codimension three loci which are
not intersections of matter curves. We describe these complications
specifically in a global SU(5) model and also their impact on the tadpole
cancellation condition.
