Estimates of star numbers are difficult to obtain. Red dwarfs are too dim to be seen as individual points so star counts cannot be obtained. The best guesses come from obtaining the mass of the galaxy and then guessing how much of that mass is made of stars. It is usually a low proportion, between 1 and 3%. You then guess how big the stars are on average to obtain a rough estimated of the star count.
Dwarf galaxies tend to have a high mass to light ratio meaning that more of their mass is in the form of dust, gas and "dark matter". Sculptor has particularly high ratio, of about 160$Upsilon_odot$, and a mass of about about 200 million times the sun.
If 1% of that mass is in the form of stars, but the stars are on average half the mass of the sun then Sculptor would have about 4 million stars. The error bars on that number are very large: The mass could be as much as 320 million suns, and the other values are guessed by me (about 3% of the milky way is in stars, but the milky way has a much lower mass to light ratio)
Perhaps the final reason that this number is not easily available is that it is of relatively little use. While the size of a galaxy can be measured spatially or by mass, and the nature of the stars is of interest, the number of them is of less use.
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