How to check if a physical document is backdated or not? Are there any labs that do it? If so, could you name a few?
I think you have been watching to much SiFi American TV
There are some labs that do them. Some forensic labs.
No clue what exactly you are asking or what you want to achieve.
https://www.unil.ch/esc/fr/home/menu...s--signat.html
It is called Questioned Documents in legal terms I guess. For instance, you are supposed to raise a claim by a certain date but you forgot to do it and then you were penalized. You could create a backdated document dated before the deadline and say that I have raised the claim before the deadline. Then the other party requests the court to verify if the document is backdated or not. The forensic people do it using ink dating technology and other advanced methods.
For time limits neither date of signing, nor date of posting the letter is important (save exceptions where date of postage stamp is relevant). Important is the date the letter was in the potential reach of the recipient (Empfangssphäre).
If you cannot proof the letter was in the potential reach of the recipient you will lose. The most common proof is the proof of delivery of a registered letter. Such a letter was in the reach of the recipient at the day they signed for it or in absent of that the first working day they could get the letter at the post office (with some exceptions extending this period to the last day they could get the letter from the post office).
In a civil case the court won't do shit. All the leg work has to be done by the claimant and defendant.
1 - he wants to backdate something in order to lie/take advantage of a situation and wants to know how likely he is to get caught, or
2- he thinks someone sent him a backdated document and would like to test it to prove the other party is in the wrong. But I'm not sure much would be gained from this in the long run, financially or otherwise.
Forensics seems utterly useless for these cases. Perhaps unless OP has decades in mind, but even then it seems very doubtful