I asked this before but did not receive and= answer. Are your scorn scores recording properly in grade book? I can not see certificate just working without the grades in grade book.
If you can't solve that then a simple workaround is to use quiz to ask one or two simple question for example did you understand the blah blahl lesson? or make your last slide say to record that you have completed this presentation go to the next assignment and choose the answer "qtip" or something that only a person who had gotten to that screen would know.