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. Never did understand the utility of this but since it's a German design there must be some reason for it.  :-) Thinking about it, the only real need is to lock out the printing keys.

For a while I thought there was a defect in the right margin of SG3s until i saw the pattern in more examples.

I've checked my SG3, it behaves like yours. Space and tab work after reaching the end of line, printing keys are locked. Mystery solved, thanks.

Laurenz van Gaalen wrote:

Update: I just discovered something interesting. After reaching the margin the printing keys are locked as explained by Michael. However, after pressing the spacebar for three times, the printing keys can be used again. My guess is that this is by design, it adds the possibility to type outside the margin without using the margin release key. This is useful when working with margin notes.

Yes, I did mention that action in my post of Dec. 10 but I did not think of the use case of margin notes. Thanks. A few more decades of this crowdsourcing and we'll have typewriters figured out.