Output to multiple files - stay unique

[Kal]

I'm outputting to multiple files based on a Data field "AccountNo".

Problem is I can have 2 or more people with the same accountNo that live in the same location.

So is there a way to keep it unique and not overwrite itself.

Maybe add a "_1 or _2 or _3" depending on how many times the same account number comes up.

FusionPro.Composition.outputFileName = Field("AccountNo") + ".pdf";

[step]

You could do it by tracking how many times each account number has been used by adding them to a global object:
JavaScript Globals

var accounts = {};

OnRecordStart

var FP = FusionPro.Composition;
var accountNumber = Field('AccountNo');
if (!accounts[accountNumber]) {
  accounts[accountNumber] = 1;
} else {
  accountNumber += '_' + ++accounts[accountNumber];
}
FP.OpenNewOutputFile(accountNumber + '.' + FP.outputFormatExtension);