I have a really old cookbook (about 1890) that calls for soured cream or sour cream in some recipes. Is this the same as the stuff you get in a tub at the store or is it like sour milk where you put vinegar in say, heavy cream??
In a cookbook that old, the sour cream referenced is probably a home-fermented variety, used as a preservation method in the days before widespread home refrigeration. You can still do this with the appropriate bacterial cultures, but most of us now buy our sour cream at the store instead. That product is similar, but made in much larger batches with a highly standardized, refined bacterial culture, producing a product with a predictable sourness and texture. Home-cultured versions are more variable, but they use similar processes on a much smaller scale.
Whether you want to call this the "same" is partly a linguistic distinction that depends on how much you want to consider the differences in scale and equipment between pre-refrigeration and modern methods.
In contrast, the addition of something sour to cream is really a substitute, used when you don't have a proper sour cream available. A cook back in the 1890s could use the same substitution then as we might today. But the production of sour cream (and all sorts of fermented milk products, such as yogurt and kefir) is much older than that, and there would have been some variety of "traditional" sour cream available, though not universally or year-round in the days before mechanized food distribution systems.