Disregarded is the past tense of disregard.
No, it is not. Discount is a verb (to mark down, to disregard) or a noun (reduction in price). The past participle (discounted) may be used as an adjective.
The past participle of "do" is "done." The past participle of "have" is "had."
The past participle of "am not" is "have not been."
The past participle of "do" is "done."
The past tense of "have" is "had," and the past participle is also "had."
The past participle of the word "have" is "had."
The past participle of "will" is "willed."
The past participle of "am, are, is" is "been."
The past participle is thought.
The past participle of "to" is "been." The past participle of "be" is also "been."
Being is the present participle. The past participle is been.