Yes, you will have done a S11 measurement for a stub to effectively measure the return loss at a given frequency.
For a trap you want to measure on a two port VNA the S21 parameters of the trap. This again will give you the parameters of the trap at the wanted frequency but instead you are measuring through loss from port to port. Calibration is important with VNA’s otherwise they tell you very big lies.
You don’t necessarily need a VNA on the lower HF bands to setup traps, a simple Sig gen and a scope will do if they are setup properly.
I don’t have a VNA at home but I do have a HP 141 with a HB return loss bridge it is very useful for making measurements on a multitude of different stuff. There are many ways to achieve what you are trying to do.
Jonathan