The two groups are considered to be identical (or nearly so) in the Christian era
TD
This is true. Even now, older ones still figure they are part of the Great Crowd and haven’t thought about it and don’t comprehend they were never part of the GC. It was always taught or believed to be true that JW were part of the GC unless they died for some reason. Even the classification prospective member of the great crowd was interpreted as: that although they were part of the crowd, it depended on not dying before the GT. So, JW believe they are part of the GC because they believe the end will come in their life time and if the end doesn’t or didn’t come in their lifetime or died of other caused, they were prospective members. The Insight Book definition I quoted in a previous post clarifies the identity of the great crowd—to be compared with personal and other beliefs. But if you are looking for a major wt study article explaining the whole thing, JW don’t do things like that. Sometimes they do but sometimes wt gradually or subtly makes change such as the Awake article on earthquakes as sign of the last days and the Insight Book explaining the length of a creative yom.
As Slim pointed out though, the doctrine is that the GC survives into the Millennium. A conclusion derived from the doctrine is that JW are part of the GC even before the great tribulation because “logically” the gc could not have appeared out of nowhere. But I agree TD, JW OS after 1935 have always believed they we’re GC.