My recollection from that era (and a view from Australia, where I recall several thousand units were sold in Australia, as "Sirius 1") was the overall number worldwide was only in some hundreds of thousands. The period it was on sale was quite limited, from early 1982 until late 1983.
As reported in InfoWorld May 1984, Victor Technologies was reorganising for bankruptcy protection and the article notes that at the time they were "Banking on Victor's survival, or at least on the continued loyalty of Victor 9000 owners (estimated by Victor to number between 100,000 and 150,000)..." .
In PC Mag Dec 1983  there is an estimate that IBM sold 188,000 PC in 1982 and 418,000 sold in 1983. As the dominant player in the market and Victor flagged as number 2 (in Europe at least) then it's numbers would be lower.
In "Business Computer Systems, Volume 4, Part 1", written in 1985, on page 31 it notes "To date, Victor 9000 sales in Europe, where the company goes by the name of Sirius exceed 100,000 units)"
Based on these references I believe we could safely bracket the sales at less than 200,000 units, and likely closer to 150,000.