“Any large-scale organization must lose some of the merits of its rudimentary beginnings. Quantity will have a coarsening effect on quality.”

No evidence that this phrasing is due to Stalin, and it does not appear in English translations of his philosphical works. Earliest English is found in 1979 in US defense industry, presumably defense consultant Thomas A. Callaghan Jr. The connection of sufficient quantitative change leading to qualitative change is found in Marxist philosophy, by Marx and Engels, drawing from Hegelian philosophy and Ancient Greek philosophy. Marx and Engels are quoted by Stalin, but this formulation appears to be a modern American form; see quantity for details.
Stalin may have said that way before World War II, there is evidence in his Russian-language books, for example here http://www.modernlib.ru/books/stalin_iosif_vissarionovich/tom_14/read_16/.
Misattributed
Variant: Quantity is quality.
Source: Re: "Quantity has a quality all its own" source? http://h-net.msu.edu/cgi-bin/logbrowse.pl?trx=vx&list=h-russia&month=1004&week=a&msg=ljEwsM4dMrpmUGVfI7EGqg, Tim Davenport, h-russia https://networks.h-net.org/h-russia, April 5, 2010

1910s, The Progressives, Past and Present (1910)
Context: Any given case must be treated on its special merits. Each community should be required to deal with all that is of merely local interest; and nothing should be undertaken by the Government of the whole country which can thus wisely be left to local management. But those functions of government which no wisdom on the part of the States will enable them satisfactorily to perform must be performed by the National Government. We are all Americans; our common interests are as broad as the continent; the most vital problems are those that affect us all alike. The regulation of big business, and therefore the control of big property in the public interest, are preeminently instances of such functions which can only be performed efficiently and wisely by the Nation; and, moreover, so far as labor is employed in connection with inter-State business, it should also be treated as a matter for the National Government. The National power over inter-State commerce warrants our dealing with such questions as employers’ liability in inter-State business, and the protection and compensation for injuries of railway employees. The National Government of right has, and must exercise its power for the protection of labor which is connected with the instrumentalities of inter-State commerce.

section 15
The Myth of Modernity (1946)

A Testament (1957)

"Corporate Man," The New York Times (22 January 1984)

Source: Reengineering management, 1995, p. 133

"China boasts of strategy to “recover” islands occupied by Philippines" in China News https://chinanews.net.au/2013/05/28/china-boasts-of-strategy-to-recover-islands-occupied-by-philippines/ (28 May 2013)

Source: The Age of Uncertainty (1977), Chapter 2, p. 84

Source: Isaiah's Job (1936), IV
Context: In any given society the Remnant are always so largely an unknown quantity. You do not know, and will never know, more than two things about them. You can be sure of those — dead sure, as our phrase is — but you will never be able to make even a respectable guess at anything else. You do not know, and will never know, who the Remnant are, nor what they are doing or will do. Two things you do know, and no more: First, that they exist; second, that they will find you. Except for these two certainties, working for the Remnant means working in impenetrable darkness; and this, I should say, is just the condition calculated most effectively to pique the interest of any prophet who is properly gifted with the imagination, insight and intellectual curiosity necessary to a successful pursuit of his trade.