JSON Schema is maturing into the de-facto schema language for JSON documents. When JSON Schema declarations evolve, the question arises how the new schema will deal with JSON documents that still adhere to the legacy schema. This is particularly crucial in the maintenance of software APIs. In this paper, we present the results of our empirical study of the first generation of tools for checking JSON Schema containment which we apply to a diverse collection of over 230 realworld schemas and their altogether 1k historic versions. We assess two such special-purpose tools w.r.t. their applicability to real-world schemas and identify weak spots. Based on this analysis, we enumerate specific open research challenges that are based on real-world problems.