An extensive study, throughout the valence region, of the electronic structure, ionization spectrum, and electron momentum distributions of norbornadiene is presented, on the ground of accurate calculations of valence one-electron and shake-up ionization energies and of the related Dyson orbitals, using one-particle Green's function (1p-GF) theory in conjunction with the so-called third-order algebraic diagrammatic construction scheme [ADC(3)]. Comparison is made with results obtained from standard (B3LYP) Kohn-Sham orbitals and measurements employing electron momentum spectroscopy, taking into account the contamination of inner- and outer-valence spectral bands by numerous shake-up states. Four relatively intense shake-up lines at 12.1, 16.4, 17.6, and 17.8 eV are found to yield recognizable spectral fingerprints in the EMS experiments. Valence bands at electron binding energies larger than 20 eV are subject to a complete breakdown of the orbital picture of ionization.