Mr. X is a very busy person engaged in both professional services and business engagements. He haphazardly filed his income tax return for the taxable year 2019 on April 10, 2020. He declared a total taxable income of 2,250,000 in the said income tax return and paid the corresponding taxes therefor. However, his accountant approached him on April 15, 2022 and mentioned about a line item in his financial statements that seem to be floating or is questionable. Then and there, Mr. X realized his error in his 2019 Income tax return. He then filed an amendment thereto immediately. Can he validly amend his tax return? why or why not? Explain fully but concisely.

Using the same facts above, but this time, unknowingly to Mr. X, his secretary received for him last April 14, 2022 a letter from the BIR which remained unopened. This letter contained a letter of authority from the BIR stating that the BIR is initiating an investigation over Mr. Xs financial books. Can Mr. X validly file his amended Income tax return on April 15, 2022? Why or why not? Explain fully but concisely.