When I go to look up a verb, very often only a few principal parts are listed. Does this mean that:
1) Those verbs are defective in the missing parts;
2) Those parts are completely regular and can be easily deduced without glossing (but luo, for example, lists all six);
3) Those particular verb forms were either never used or were rare enough that no examples survive; or
4) Something else?
This is a dumb ...