Did it list the creditor or any dates?
Was this creditor ever on your report?
As for the size..........I've heard of $200 debts being $2000 debts due to fees and penalties.
You need to DV, this keeps them from reporting until they validate. SOL is important to know, but if it isn't on your report and you don't remember it for sure, it is going to be hard to know this.
You can try calling the OC and get some information if the letter provided an account #. I feel safe calling OC's, but not CAs. OC's are less likely to lie/deceive.