Thus, PSS would mean “postscript script”, which doesn’t really make sense in this context. Rather, the correct way to write this abbreviation is “PPS” for “post-postscript” or “after what comes after the writing”. This continues to PPPS, PPPPS, and so on.
Also note, both forms “P.S.” and “PS” are considered correct, though the latter form, without the periods, is considered the preferred method today as “postscript” is now considered one word.
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