#It is possible for a patron not to know their warlock

As you quote in your question:

The Great Old One might be unaware of your existence

And, as I assume you are aware based on your use of that quote:

###Otherworldly Patron

At 1st level, you have struck a bargain with an otherworldly being of your choice: the Archfey, the Fiend, or the Great Old One

Ergo you explicitly can have a patron who is unaware of your character's existence.

It is possible for a patron not to know their warlock

As you quote in your question:

The Great Old One might be unaware of your existence

And, as I assume you are aware based on your use of that quote:

Otherworldly Patron

At 1st level, you have struck a bargain with an otherworldly being of your choice: the Archfey, the Fiend, or the Great Old One

Ergo you explicitly can have a patron who is unaware of your character's existence.