I've been hesitant to make available a modified copy of Ralph's spreadsheet, because of the risk that I've made a mistake, and problems resulting from that could end up being blamed on him. That's why I chose to just describe the changes I made to fix the bug I found.
I've now modified a new copy of the old spreadsheet with those formula changes, and made it available on my own web site, with text explaining what changes I've made, and why. The copy also has a prominent statement on the first page saying that it has been modified, and pointing at the web page.
The page is at https://hamartun.priv.no/filmtest.html.
Ralph: I hope this is OK - let me know if you have any objections!