It isn’t actually all that small a change, if the 1949 figure is the one used on my vintage 1959 edition map then in old money they determined it as 4406 feet. According to the article the redetermination is 4411 feet 2 inches so the new height is some 5 feet higher.
Since 1949 the sea level has risen nineteen centimetres, taking nearly eight inches off the new height if true sea level is used rather than the OS datum sea level. Taking the difference between the highest and the lowest projected sea level rises the Ben will be back to 4406 feet somewhere between 2090 and 2200.
“A bit dodgy”? I would rather say horrendously complex! The water can “slosh” about on a multi-decadal time scale, changing currents can affect the level, and isostatic compensation for loss of ice overburden is much slower than the melt rate of the ice caps - witness that some areas (such as the Baltic) are still rising after the melting of the Ice Age caps. If the North Atlantic Drift slows then local sea level around the UK might fall even though the Global average may rise sharply. I think my generalisation is valid but we will have to see!
