Simeon is not mentioned
<p><b>And let not his men be few—</b>It is possible that this clause belongs to Simeon. In the Alexandrian copy of the Septuagint the clause stands thus: Και Συμεων εστω πολυς εν αριτμῳ, "and let Simeon be very numerous", but none of the other versions insert the word. </p>
<p>
As the negative particle "let not his men be few" is not in the Hebrew, but is supplied in our translation, and the word Simeon is found in one of the most ancient and most authentic copies of the Septuagint version; and as Simeon is nowhere else mentioned here, if not implied in this place, probably the clause anciently stood: "Let Reuben live, and not die; but let the men of Simeon be few". </p>
<p>
That this tribe was small when compared with the rest, and with what it once was, is evident enough from the first census, taken after they came out of Egypt, and that in the plains of Moab nearly forty years after. In the first, Simeon was 59,300; in the last, 22,200, a decrease of 37,100 men!
Adam Clarke's Commentary.</p>