Okay... You looked on Speedway Researcher, didn't you? At Poole 1972?
We were talking about Speedway Researcher recently, and I did mention that there is information missing (certainly not the fault of anyone involved with the site), and also, that not everything is cross-indexed.
Instead of going to the Poole archives (which I figured you'd checked), I searched by year, and then Season Results. It was in there, but not in the Poole file! So, whenever you want to check something on there, check ALL possible locations, as they don't always appear where you first look.
The interesting thing here is that there was a note attached. The meeting was never advertised - and never reported on - in Speedway Star.