My point is the value of these stamps has not really kept up with inflation. Take the 4x$25 mint revenue stamps issued in 1894 for instance. $100 in 1894 in NB was a large sum of money. Apparently, the annual pay of a postal clerk in 1900 was $360. The local postage rate in 1894 was 2c per half oz. The equivalent nowadays is 60c which means the $100 would be equivalent to MYR3,000 today. Using the British retail index in our calculation would yield a figure of MYR5,000. This block of 4 mint stamps should cost a lot less than MYR500 to buy today. All together, it was a very bad investment.
A similar situation would apply to the 1948 4x$10 which would be equivalent to MYR300 today using relative postage rates. But using the British retail index would give an equivalent of MYR1,120 due to recent decades of high inflation. This block of 4x$10 is probably worth less than MYR350.
I am assuming the stamps were paid for at face value at the time of issue.