We studied LaAlO3/SrTiO3 interfaces for varying LaAlO3 thickness by core-level photoemission spectroscopy. In Ti 2p spectra for conducting n-type interfaces, Ti3+ signals appeared, which were absent for insulating p-type interfaces. The Ti3+ signals increased with LaAlO3 thickness, but started well below the critical thickness of 4 unit cells for metallic transport. Core-level shifts with LaAlO3 thickness were much smaller than predicted by the polar catastrophe model. We attribute these observations to surface defects/adsorbates providing charges to the interface even below the critical thickness. Show Partial Abstract