My experience is different. The 298 I use matches Mikes swatches and also matches a No 9 aerial base I just unwrapped. The latter is one of a batch I bought many years ago, all sealed. Most were green, some were brown so unlikely to be post 1960's repaint and packs. I have seen more variation in modern interpretation of BS298 than exist in what I have just described.
The same applies to Service Brown BS499. In a matt finish, I'm happy it matches SCC2 very closely, others disagree but with brown in particular, gloss level makes a huge difference to the perceived colour.
If modern paint manufactures cant always perfectly match each others colours, I'm not sure why some are so sure of the accuracy of colour 80 years ago. I'm also not convinced that when BS381 was expanded post war, they decided to very slightly change some of the colours whilst retaining the same names!