I have a pot from a few years back about half full. Is it ok to use or do I need new every time I dip them .

Use it.

I use same wax pot year after year, just add new each time. Only time ive changed it is when it had a large amount of debris fall into pot of hot wax and I ordered new blocks of wax once that smelled like the cotton candy stand and catch rate that year was affected. Not sure why that wax smelled so sweet but it was very strong sweet smell. Ive never noticed a difference in catch rate from used wax and new wax that didnt start of with a odor. I do make a point to keep wax clean while storing also with plastic wrap over top of pot and lid on it. Just my experience, sure others will give you more advice.

Store your existing pot of wax in a very good sealed container. Just like waxed traps wax will absorb odors from all kinds of things like gas, oil, solvents, smoke and just about anything that omits and odor.
I add new bars of wax to my existing pot. If the wax is getting pretty dirty I will scrap in and start a new.
Pressure washing or cleaning your traps before dying and waxing is a good idea.