In most countries you do not get to keep accidentally transferred funds and attempting to do so can constitute theft. If you receive money you know you shouldn't have, call the bank, don't spend it.
9 months is well within the regular window too. Would be different if it showed up 10 years later.
Their first reaction was mostly “well this is weird, I guess Revlon decided to pay off the loan rather than fight about it.” Their second reaction, after Citi sent them frantic notices saying it was a mistake, was to send each other Bloomberg chat messages making fun of Citi. Their third reaction, after some more serious reflection, was to say “we are keeping the money, see you in court.” All of these reactions were pretty reasonable and worked out well for them.
[1] https://www.tandfonline.com/doi/full/10.1080/09615768.2022.2...
It's six years in the UK.
This is why you should retain six years of bank statements...... and a 'bank error in your favour'? You had better wait six years before you spend the dosh.
[Though to be pedantic, in law you still owe the money, just that after six years without any attempt to reclaim it, the debt becomes legally unenforceable]