There is an argument to be made that pure traditional butter is inherently kosher as milk from non-kosher animals won't congeal properly. Modern butter plants at times utilize whey left over from cheese production as a substitute for costly butterfat when making butter, and Rav Moshe Feinstein went so far as to argue that butter incorporating whey from non-kosher cheese was still kosher. (See OK Kosher's discussion here http://www.ok.org/isitkosher/is-butterkosher)
If you want to hold by the above, any dairy butter will be kosher "year round and for Passover", certainly including butter with any type of kosher supervision whatsoever. If you do not want to hold by the above, you will have to talk to the Triangle-k people and see what their process is and if it satisfies you.
One final note: given that dairy butter has no reason to contain chametz or kitniyot and is not commonly processed in plants where chametz is processed, why not just buy a standard "year round" kosher butter certified by a hechescher of your choosing?