We have cases when for some reason artifacts gets lost from storage, even if those are required for building. For example:
https://testresults.qt.io/coin/integration/pyside/pyside-setup/tasks/1512314942

No binary artifacts for "/home/vmbuilder/ci-working-dir/storage/qt/qtbase/209bb9b26db15b6673003cac1ff8fa69c5886215/LinuxRHEL_6_6x86_64LinuxRHEL_6_6x86_64GCCqtci-linux-RHEL-6.6-x86_64-a4584eRelease_NoUseGoldLinker/2a48a3b7dcb9652b1532a3ad14de7580b5b9b1ee/build_1506108045/artifacts.tar.gz" skipping

details in:
https://testresults.qt.io/logs/pyside/pyside-setup/f1c8b5ee5de685590a5a9d8cdd526959d03952b0/LinuxRHEL_6_6x86_64LinuxRHEL_6_6x86_64GCCqtci-linux-RHEL-6.6-x86_64-a4584eRelease_NoUseGoldLinker/ac8cc81debc09de4f89f98336dbf6f548b7af908/build_1512314950/log.txt.gz

Instead of just skipping the extraction, we should build the missing artifacts. While this is not done, there is no way to re-create the missing files, except manually deleting build_success files from storage. That can be quite laborious task especially if all qt5 artifacts from all configurations are missing.