There is no validity limitation on ATA 104 level III courses. As long as it covers all the Chapters.....and as you mentioned you did have company Approval to sign for the Type.....So basically it all depends on the next company's Policy on granting Approvals....they might give it to you straightaway as long as you are Current on the type....or in the worst case scenario...they might ask you to get a refresher course.....but answering the Basic question.....there is no validity or Time Limit on your course (as far I know)!!!