Panels also have a tolerance of eg +/- 3% this varies from panel to panel!
I would expect that all panels in the array would need to be operating at that higher level, otherwise the array woudl run at the ability of the weakest link.
The KV's in my array are stated to be 0 to +5 W tolerance, and are sold as a variety of models, simply sorted by their "flash" test at the factory. For example, there's KV240 (240-244.9W), KV245 (245-249.9W), KV250 (250-254.9W) panels which are identical, other than some had a higher flash test output than others and have been sold at a better price.
But the output, as mentioned earlier, is quoted under standard conditions of light and temperature.
A few days ago, when my KV250's approached 265W, but it was a very sunny, very clear, cool and breezy day. The sun was probably as strong as standard test conditions, but it was cooler and breezier, which probably helped boost the output of the panels compared to a hot day.