How was the completeness theorem of propositional logic proved in the first place?

Question

the completeness theorem of propositional logic is one of most basic theorems which undergraduates learn about logic.

as long as I understand, it is common that the theorem is proved by means of Henkin.

But Henkin's proof didn't exist before 1949.

Then how was the completeness theorem of propositional logic proved in the first place?

I tried to find such a non-Henkin proof, but I couldn't.

Thanks!