If (it has) modest sales

One now-common innovation McGregor pioneered was that of the self-contained, multi-issue story arc.^{http://en.wikipedia.org/wiki/Jungle_Action#cite_note-sacks-6} The first, "Panther's Rage", ran through the first 13 issues,^{http://en.wikipedia.org/wiki/Jungle_Action#cite_note-Top10-15} initially as 13- to 15-page stories. Starting with Jungle Action #14, they were expanded to 18- to 19-page stories; there was additionally a 17-page epilogue. The length of the story arc coupled with the series' bimonthly schedule made it difficult for readers to keep characters and subplots fresh in their memories, but Jungle Action nonetheless maintained passable if modest sales and was popular with the desirable college-student demographic.^{http://en.wikipedia.org/wiki/Jungle_Action#cite_note-Back27-10} Two decades later, writer http://en.wikipedia.org/wiki/ChristopherPriest(comic_book_writer)'s 1998 series The Black Panther utilized http://en.wikipedia.org/wiki/Erik_Killmonger, http://en.wikipedia.org/wiki/Venomm, and other characters introduced in this arc.

I'd like to know whether "it has" has been omitted after "if."
Thank you, in advance, for your help.