It is very difficult to truly assess skill level. Standardized testing, degrees and certifications don’t tell the whole story. Management reviews can undersell themselves. As a result, managers and marketing teams are often understaffed and ill-prepared for certain levels of work, and the results generally show it.
You should know your true level, for a variety of reasons. Most importantly, it empowers you to be practical about what type of work you are best suited to execute well and allows you to focus on what skills you need to develop.