German Employment Contract When Is A German Employment Contract Binding, If It Does NOT Mention An Effective Date?

When is a German employment contract binding, if it does NOT mention an Effective Date? - german employment contract

When the German is a binding contract, if no date of effect mentioned?

Which of the following is the actual date:

a) the day the signs of employers, both the originals?
b) A few days later, after the new contracts on the home page of an employee of another city ()?
c) A few days later, when the employee signed the contract shortly before the employer?
d) the original contract signed back in the position of the employer?

If (d), this means that the employer withdraw the nomination May / contract, although he signed?

Under the assumption that there are about a week in bewteen 3-4 weeks between each stage (a) and (d).

Thank you for your advice!