Sales and the installed base
The sales figures that carry a real citation — SPA certifications and Brøderbund's own revenue disclosures — set apart from the rounder numbers that don't.
Sales figures for the original 1985 game are unusually well documented because the Software Publishers Association (SPA) certified them as sales milestones were hit: past 500,000 units by April 1989, past 800,000 by December 1989, past 2 million by 1991, and past 4 million by 1995. That run alone makes it, by a wide margin, the best-known number in the franchise's history.
What Brøderbund itself reported
At the company's November 1991 IPO, Brøderbund disclosed that The Print Shop made up about 33% of revenue and the Carmen Sandiego line about 26%. For fiscal 1992, with company-wide revenue at $75 million and earnings at $9.65 million, Carmen Sandiego titles were reported as roughly 25% of revenue on their own, and cumulative franchise sales were reported to have passed 2.5 million units that year. Across the games' first decade, the two lines together — Print Shop and Carmen Sandiego — are reported to have made up well over half of Brøderbund's yearly revenue.
Where the record gets soft
Beyond those disclosed figures, later round numbers circulate widely — claims of five million or more units “sold into schools and homes worldwide” by the late 1990s turn up repeatedly online — but none of them traces back to a citable primary source in the research for this entry, and the 2.5-million franchise figure for 1992 doesn't obviously reconcile with the 2-million figure SPA had already certified for the first game alone by 1991. Rather than average those numbers into a false precision, it's more honest to say: the 1985 game's own sales are well documented into the mid-1990s, Brøderbund's revenue split is on the record for 1991–92, and no reliable, sourced total exists for units sold across all twelve games combined.