Where is ">G7USM1/27-197 [subseq from] G7USM1" coming from, both when you turn it into a hash key, and later when you check for the key's existence? Is it possible that it is as simple an issue as always chomping your input, so that you're storing hash keys without trailing newlines, and so that the strings you're testing have no trailing newlines? Was the document from which you've derived these keys generated on a different operating system so that there's a line-ending mismatch?