I changed a lot of different jobs and for different reasons. But what I can tell you is: most employers just look at your documents, and if they check knowledge, that is very superficial.
It happens in different ways. In large companies, people are checked very carefully. Even in the case of providing a detailed portfolio and recommendations.
When I worked in USA the most important thing was recommendations and they are alweys checked. In Russia recommentations means nothing. Diplomas are important for state jobs. Many people have a diploma but do not work acording the proffesion.