There are cases that Jar file contains more packages with different versions like e.g. xml-apis.jar or XercesImpl.jar. Tattletale has in reports only first Specification-Version value. There should be all versions shown in key -> value pairs (package as key and Implementation and Specification version both, if exists, as value)
There are not only Specification-Version, but also Implementation-Version frequently used in jar manifest jars to identify package versioning. See at point "attributes defined for extension and package versioning and sealing information" at http://java.sun.com/j2se/1.5.0/docs/guide/jar/jar.html#JAR%20Manifest or the same for java 6 http://java.sun.com/javase/6/docs/technotes/guides/jar/jar.html#JAR%20Manifest.