A lot of verbs have both the formed that ends on "ed" and one that ends on "t" like your example. Often it makes not difference at all which you use in the perfect or pluperfect.
If you are not a grammar geek that means when you say or write I have passed it or I had passed it. Most of us say whatever feels most natural. I usually say I learnt something, but sometimes I hear myself saying I learned that.
I tend( I think) to say I have passed and to use past as the noun , as in: "In the past the t-form of the verb was considered incorrect, now we use both forms."
I believe that statement is true and have certainly always told my pupils to use the form they were most comfortable with. Pointing out at the same time that it is not good English to say or write "I past him in the street", you have to say and write "I passed him in the street"