Subsequent change in compensation

[ombskid]

Sole proprietor filed tax return and made profit sharing contribution based on net sch c income. Later the accountant finds a mistake and income was 50k or so lower. The return is amended. The amended income would significantly reduce allowable contribution.

The deduction for the contribution must get reduced in the amended filing, correct?

If the contribution was made after the end of the plan year, there is no penalty for over contributing, at least as far as that particular year, correct?

What penalties would apply and or corrections can be made if the contribution was made during the year being corrected?