I may not have presented this well in the original comment. This wouldn't be generating random static cards to put into an Anki deck, but a separate system which dynamically presents expressions made up of known components, and tracks those components instead of specific cards. It seems plausible to restrict these expressions to those composed of notation you've already encountered.

In fact, this could work to its advantage. It also seems plausible to determine which components are bottlenecks, and therefore which concepts are the most effective point of intervention for the person studying. If the user hasn't learned, say, hat-and-tilde notation for estimators, and introducing that notation would result in a greater order of available expressions than the next most bottleneck-y piece of notation, it could prompt the user with "hey, this is hat-and-tilde notation for estimators, and it's stopping you from reading a bunch of stuff". It could then direct them to some appropriate material on the subject.