It seems logical, but still, my experience is the complete opposite. I think that it is an inherent problem with the technology. "Upgrade from Library v4 to Library v5" probably heavily triggers all the weights related to "Library," which most likely is a cocktail of all the training data from all the versions (makes me wonder how LLMs are even as good as they are at writing code with one version consistently - I assume because the weights related to a particular version become reinforced by every token matching the syntax of a particular version - and I guess this is the problem for those kinds of tasks).

For the (complex) upgrade use case, LLMs fail completely in my tests. I think in this case, the only way it can succeed is by searching (and finding!) for an explicit upgrade guide that describes how to upgrade from version v4 to v5 with all the edge cases relevant for your project in it.

More often than not, a guide like this just does not exist. And then you need (human?) ingenuity, not just "rename `oldMethodName` to `newMethodName` (when talking about a major upgrade like Angular 0 to Angular X or Vue 2 to Vue 3 and so on).