Previously, the script was caching any file already present in the destination directory, regardless of its origin. This caused issues when the directory contained files copied from external sources like `autoreconf --install`. For example: 1. `./autogen.sh --install` copies `config.guess` and `config.sub` from the system to `./tool`. 2. `ruby tool/downloader.rb -d tool -e gnu config.guess config.sub` treats those files as if they were downloaded and caches them. 3. Removing the files: `rm tool/config.guess tool/config.sub`. 4. Running the downloader again, it mistakenly restores the cached files instead of downloading fresh versions.