Then one becomes a Haupt and other Neben, you still anmelden and never have to abmelden unless you move out of the country.

it is required no matter what.

It is blocked, you cannot get it back all at once.

It is valid until as long as humans exist (for now).

Don't agree at all with this answer. It could also be "held an employment". It is firm evidence enough if you have an unbefristet contract, without Probezeit . Bouncing jobs has no significance, you do not speak for the German state. And the application date is not October 15, you can apply even today if you wanted to! But it wont be processed before October 15.

This information is correct.

Nobody reads such long questions on a website where new users like you hardly upvote answers (think what incentive do people have who answer?)

Did you try? How did it go?

Thanks for upvoting and accepting the answer ;). The date you start working is written on the contract. You can have a contract starting the next day after your Masters completion, for example.