The ContentEntityObject.getAttachmentNamed(String name) simply returns the first occurance of the attachment with the given name from the list of attachments. This may not always be the newest version. When working on the calendar plugin I encountered a case where the version order in the attachments for a file were [v2, v1, v3]. Version 2 of the attachment was always returned from the getAttachmentNamed() method instead of the expected version 3.