Distinguishing the semantics of a language from its syntax means (at least) distinguishing the meaning of the expressions (what is being represented) from the grammatical structure and formation rules (the means of formal representation).
Distinguishing object and meta language means distinguishing a language that is being talked about (the object language) from the language being used to do so (the meta language).
Both distinctions are claimed to have emerged in the very late 1920's, in particular with Gödel's incompleteness papers and Tarski's undefinability theorem.
My question is:
Is it possible to have drawn one of these distinctions with acuity, whilst ignoring the other, or (more likely) what aspect of the historical development led to their simultaneous recognition? In other words, what sorts of relations hold between the two distinctions that would compel an early researcher to recognize both, if he or she were to recognize one?