Richie,
There are several possible approaches to collections of commonplaces.

1. If they are a complete mixture it's best to treat them as an unique composition.

2. If they have a majority from a recognised autonomous song then classify them with that song noting the additions.

3. For study purposes it is usual to include a mixture as a version of all the songs that contributed to it.

I realise though with songs like this such decisions are far from simple.

When dealing with versions recorded by revival singers like Isla you need to be aware they often mix and match themselves which is why we always try to go back to their sources. Personally I don't include versions by revival singers in my main study index. This is not a qualitative decision as often the redactions of revival singers make superb songs.