no deductions, they made one mistake, so a one place penalty on the final league table seems like enough. ;);)
But seriously, sounds like admin issues rather than shenanigans based on the current information.
it does if there are 10 of these scenarios
also, you have to remember that a 100% of a sale counts towards FFP, so they just need to sell 1 or 2 fringe players each season to offset that years FFP burden