I wrote to Channel 4 under the FOI act requesting if they could fill the gaps in our database. After Channel 4 refused, I asked why and asked if they could go into detail.
The upshot of the reply was that Channel 4 does not have the information, so don't try asking yourself.
[...] we can confirm that Channel 4 does not hold this information in aggregate form. Countdown was the first programme shown on Channel 4, when it began broadcasting in November 1982. Since then thousands of episodes have been transmitted over a period of 31 years. As you have noted, some of the information you have requested is available, but not all of it. Accordingly, were we to attempt to collect all the information we would be required to search every script for every episode and cross-check these against what was broadcast. This would involve months of work. Accordingly, even were this information within the
scope of the Act, responding to your request would far exceed the Act’s costs threshold appropriate to Channel Four Television Corporation.