Good info.
I have sold some liqour to a couple of kalong guni and spoke to them too. They told me, the older the liquor is, the more valuable they are due to better taste from aging. The better entertainment outlets (and some individuals too) actually want to buy and keep these old liquor so that whenever a rich and generous customer wants to entertain his friends, he will call for the older liquors, and that is where the outlets make big bucks. That is also why the kalong guni and outlets want to have the original packing and boxes to show that these are genuine old stuff, not some mao pai stuff. I remember when I sold my old bottle of Martell XO to the kalong guni, he kept on looking at the label and cap on the bottle and compared it to the picture on the original box to see if they were the same. He even examined the label on the bottle to see if he could detect if the label was original and not just a printed & added on one.
Of course the kalong guni is a businessman and will try to buy in your liquor at prices as low as possible so that he can go and sell it at a higher price to a dealer or if he has the contacts, an entertainment outlet directly. As mentioned, the NTUC or Cold Storage liquor prices are indicative and these are for newly aged liquor, not old ones. I believe you can sell your liquor at prices comparable, if not higher than what NTUC or Cold Storage is selling for the same brand & size of liquor for your long time liquor.
Whatever it may be, you decide if the price offered is right and sell accordingly.
Cheers!