[2] Symbols usage is sometimes idiosyncratic to engineering disciplines, and national or local variations to international standards exist.
It is very common for potentiometer and rheostat symbols to be used for many types of variable resistors and trimmers.
The words anode and cathode aren't part of the diode symbols.
"K" is often used instead of "C", because the origin of the word cathode is kathodos, and to avoid confusion with "C" for capacitors in silkscreen of printed circuit boards.
[6] Note: The pin letters B/C/E and G/D/S aren't part of the transistor symbols.
Depending on the IC, the two-input gates below may have: 1) two or more inputs; 2) infrequently some have a second inverted Q output too.
For the symbols below: Q is output, Q is inverted output, E is enable input, internal triangle shape is clock input, S is Set, R is Reset (some datasheets use clear (CLR) instead of reset along the bottom).