The assessment of your educational credentials works on a lot of factors which are evaluated by specialized agencies like the WES. I, or anyone else giving your an advise, unless someone who has done the same program, would be just making a speculation. I would advise you to apply for your WES assessment to get a sure result.
Based upon the information you have provided, and taking into account that the program was for 6 semesters (3 years), which you finished early as you were given credit or advanced standing for your bachelors degree, I would say it should be accessed as a 3 year diploma. I see it as a degree program which you finish faster as you have done the coursework and you get credit for it, or you finish it early by taking extra credits each semester will not impact the duration of your program.
However, to be sure, you should apply for an assessment and see what the results are.
This is not too helpful, but I cannot provide you with information which is beyond my area of knowledge and expertise.
