I am flabbergasted that people find their lack of detailed rule understanding surprising. I rarely play with people that know the rules incredibly well. I'm in games with nearly 20 people right now ... and very few of them understand the invisibility rules. Few of them know what their spells do by heart. Few of them remember the fine details on their abilities, especially when they're conditionally relevant.
I find the group to be pretty typical of their rule mastery. Two with great knowledge (Matt an Liam), a few pretty good (Taliesin, Laura, Travia, Marisha (now)), and a couple that rely upon others (Sam and Ashley).
I think people find it surprising that they still don’t know them after playing almost weekly for five years, and making six figures playing D&D.