Because the figures $$\left.\text{}^{6}_{5}\right.$$, $$\left.\text{}^{4}_{3}\right.$$, and $$\left.\text{}^{4}_{2}\right.$$ are only used for seventh chords, the “7” is omitted when labeling inverted seventh chords.
Notice that it is essential with seventh chords to include symbols like “M” (for a major seventh chord) and $$\left.\text{}^{\circ}{}\right.$$ and $$\left.\text{}^ø{}\right.$$ before the figured bass numbers and after the Roman numeral.