A WSDL can import and include other WSDL and XSD files as well as the included WSLDs and XSDs can.
If you run the wsimport task and then modify one of the included files or files included by the included files, that task is up-to-date or taken from the cache.
The files need to be searched recursively for included or imported files and all those files must be defined as input file for the task.