My son has bought new primed cast iron drain pipes to replace the 120yo ones that have rusted away. He wanted to match the original paint, which was a sort of matt white. I went to a local supplier who provided 5L "Johnstone's flat oil-based brilliant white".
Son painted 2 coats in his garage and said the paint seemed excellent, and I admired the results when I visited.
Then on Monday he finally read what it said on the tin and sent me an email expressing, shall we say, dismay. The tin and the datasheet say
"A solvent-borne, traditional matt finish formulated for interior use. Based on an alkyd resin it provides excellent obliteration and flow characteristics and produces a smooth even finish with excellent durability".
I rang and spoke to the Johntone's technical support desk, who said the formulation was exactly what they would use for an exterior paint, and the reason it said "Interior" was that getting it independently certified for "Exterior" was a long and expensive process, so hadn't be done for this paint. I then asked about yellowing and they said that yellowing would only take place in low light conditions indoors eg on skirting boards and that the paint would be fine used externally in natural UV light.
So we have a paint sold as interior that is better as an exterior paint.
I blame the EU.