It may not be apparent from the cumulative figures, but Broadway sales took baby-steps toward a rebound during Week 18 (Sept. 24-30), with nearly every show on the boards posting gains.Looking at the overall totals, B.O. was up less than $100,000 to $17.2 million for the 22 shows on the boards. But that’s because all the week’s upticks were countered by the loss of “Porgy and Bess,” which shuttered Sept. 23. Nonetheless, almost every production improved compared with the previous frame, which saw sales slump in a September sesh that wasn’t boosted by the 2-for-1 ticket deals of the recently-ended Broadway Week. The week’s biggest increase came from “Bring It On” ($485,269), up 31% in a bump that suggests the show might be gaining a bit of autumn momentum now that the back-to-school distractions of early September are past. The recently opened “Chaplin” ($498,568) also gathered steam. “The Book of Mormon” ($1,636,331) remained king of the hill, besting more-frequent top dogs “The Lion King” ($1,600,129) and “Wicked” ($1,536,124). Overall Rialto attendance inched up by about 1,000 to 184,210. That’s way down from the 207,794 posted during the same week in 2011, but that frame benefitted from the aforementioned Broadway Week initiative, which in 2011 ran through the end of September. The 16 musicals grossed $15,254,958 for 88.9% of the Broadway total, with attendance of 152,251 and an average paid admission of $100.20. The six plays grossed $1,911,505 for 11.1% of the Broadway total, with attendance of 31,959 and an average paid admission of $59.81.