80C Related

I don't think so because the said section says that amount should be paid/deposited in the PY.

80C. (1) In computing the total income of an assessee, being an individual or a Hindu undivided family, there shall be deducted, in accordance with and subject to the provisions of this section, the whole of the amount paid or deposited in the previous year, being the aggregate of the sums referred to in sub-section (2), as does not exceed one hundred and fifty thousand rupees.

Yes agree with the above view. 

Only last year's deposit can be considered for 80 deduction.

No. Only the amount deposited during the Current Financial Year (F.Y.2019-20) is eligible for deduction u/s 80C. Amount deposited during previous Financial Years will not be eligible for deduction even though you have not claimed earlier.

Current FY 2019-2020 you can definitely take 80C deduction while filing ITR.

For FY 2018-2019 , you can file revised return upto 31-3-2020 (no late fee apply) under 139(5) and claim 80C deduction.

You can file revised return for FY 2018-2019 , even if you have received intimation under 143(1).

For earlier 2 years, you can not file Revised return and 80C deduction gone waste