You should focus on the error message.
you wrote "System throws message as document type "SA" is not defined."
I doubt that SAP would issue a message about a wrong document type if the reason would be the document date.
The document date may come up as next error, after the initial error is fixed, but before you can be certain, you have to fix the problem with the document type.
Further you should post the original message, unmodified, along with the message number