Important to keep in mind that any "standard atmosphere" is not intended to be a strict representation of the atmosphere as such ... rather an idealised set of numbers which, coincidentally, may bear some relationship to what might be seen in the real atmosphere from time to time in particular places.
As we all understand, the real atmosphere varies regularly and significantly from the ISA idealisation. ISA, if my recollection is correct, is based on North American continental met records from many years ago.
It is worth noting that there is a number of such standard atmospheres defined and in use within the test fraternity.
Two considerations to observe ..
(a) for test or certification work, one might want to use a particular standard atmosphere to suit a defined requirement. This is more likely to be seen in the military world.
(b) for civil work, the main significance of the ISA is that it provides a reference atmosphere for resolving actual test data and comparing aircraft on an apples vs apples basis