It's been in a bowser - the issue is that bowsers and not drums are vented - most modern vents are pressure activated.
When the stuff expands, the "high notes" evaporate first and this reduces the RVP (Reid vapour pressure) which makes the stuff less potent that the spec it came out of the refinery with.
Would I use it - yes but only after I'd sent a sample back to Grangemouth and asked them to test the RVP.
My fairly basic lab in E Africa had the kit for testing this as the temperature extremes were higher, I'd naturally have any shipment tested and compare with the refinery spec. Most of my Avgas came from Italy or from Durban. As I had no idea how long it had been in storage, a full test was standard acceptance procedure.
It will burn the exhaust valves in automotive engines if used neat and for a long time....
Stik