I missed the deadline to claim my dependent care FSA for a previous year. Since the entire FSA amount was forfeited, can I claim dependent care credit instead for that year ?
No. You already received the deduction, since that lost FSA money was pre-tax. You can't double dip. However if your FSA amount was less than your actual expenses, you can file on the difference.
Example: $4500 actual expenses, $3000 FSA (lost). You can get the dependent care credit based on $1500.