I found it in an old Italian typewriting course that I’m studying, it says translated “on olivetti machines both manual and electric , if you press the margin release key while performing line return, the carriage will stop ten spaces before the set left margin. This creates a fix indentation useful for starting new paragraphs”

On an SG1 and an SG3 here, the right margin stop locks the printing keys as expected at x characters after the bell but not the spacebar nor tab, which both ring the bell and then blow right past the margin stop. Additionally, when the End-Of-Line lock stops the printing keys, I can continue spacing past the margin and then after about three spaces on the SG1 and about eight on the SG3 the printing keys are again active.