However, where lay persons write contracts themselves or download a from the internet, often these legal niceties are lost upon them.
In practice the courts are more sympathetic than one might anticipate.
Live camera vrijen amateur - Backdating document
The risks of backdating (or misdating) documents accidentally is multiplied in modern commercial transactions by the practice of getting all the documents signed before "completion" and then rushing around dating them afterwards.
My father (who was also a lawyer) used to love telling a story about how he was able to triumphantly prove to the court that a yacht charter was backdated by showing the stamps which had been used to pay the nominal 15 stamp duty were in fact first issued by the post office some four months after the date stated on the face of the document.
Another common example is where one person purports to sign a document on behalf of another person, and then afterwards the parties execute a backdated power of attorney to clothe the signatory with the necessary authority.
In practice what should happen is that the principal should ratify the signatory's act as agent, and the courts are usually happen to construe signing a backdated power of attorney as misguided (but effective) attempt to ratify by conduct.
The first and most important thing to note about the consequences of backdating a document is that it is potentially a criminal offence.