I read unvalidated into one variable and then put it into a validated variable when I call the validation routine. The variables differ only in their prefix. I learned this from https://www.joelonsoftware.com/2005/05/11/making-wrong-code-look-wrong/, which is still worth reading. Here's a pseudocode example:

my $inv_data = get_input();
my $val_data = val_from_inv($inv_data);
[download]

Regards,

John Davies