While the modelling of electromagnetic field coupling through apertures constitutes a well-known problem class in electromagnetic theory, it still is a nontrivial problem to determine accurate electromagnetic field solutions for specific cases of aperture coupling. In this contribution this circumstance is illustrated by a number of explicit examples which are, in increasing order of complexity, given by single circular apertures in planar shields, single circular apertures in rectangular cavities, and by an aperture array within a rectangular cavity. It is seen that both analytic solutions and numerical standard methods exhibit restrictions due to their approximative character in terms of validity and discretization, respectively. As a result it is concluded that, depending on the type of problem, standard solution techniques still are limited for accurately predicting aperture coupling such that refined hybrid numerical methods become required.