They can also include where the coin was found and in context. Like Ground zero coins from 9/11.
You'd need a way to prove it but don't know how that would work.
Boor war site find could add numismatic value to your coin, maybe more than you think. Or could add more value to the coin than the coins numismatic value alone.
You might need an archeologist buddy to help you as a witness and testiment or maybe it's one of those things you just have to trust from a relliable person.
Ultimately it's whatever sells the coin that makes it valueable. If someone want's it for a reason it's valuable.
The thing is there's no way to predict what crazyness catches on at what time. Markets have been trying to create the context for value but nothing beats crazy.
Some markets have some success mainstream as with silver dollars and maple leafs or good old krugers but some don't do as well, for instance the marketed Mandela R5 coins.
Someone buys one for R90 000 and a few years later someone sells them by the dosen for R50 each. Scarcity is also a factor, well there where a few billion or million of those R5 coins made, but that can change again and again. You could also try buying them from whoever was reserving them from circulation and destroy them all. Contextual coins adds to scarcity.
However there's nothing wrong with numismatic quality, looking for good coins or the odd super perfect coin and having it graded and sealed to perfection. Or someone who can be trusted to have people be sure that what they are buying is what it says it is. Or having all the troublesome "convincing of athenticity" work over and done with. Without an authority like that alot of numismatic stuff would not work. You need a "banker" that follows the rules in a game of Monopoly.
Chances are an initiative like SANGS, for them to really pick up would need to meet the existing authority's standards(Maybe they do). An authorisation and licence to make the banker concept hold together. Not in competittion but in agreement and cross recognition and possibly a statement of that recognition. NCG might not recognise value that SANGS does and vice versa but they need or might have a common ground.
There's also DIY grading. Not everyone is into authority and can recognise a coin on the old primitave scale from Poor to Very Fine without needing one. Coins eschange cheaper that way and just for the sake of collecting, however when you have eventually come to recognise the value of some of your collection you would probably do youself a favour both getting it sealed for preservation and graded at the same time. Some coins are just hard to find in proof or very fine condittion. At some point of time no one thaught theyd be worth anything and maybe if they did they wouldn't have been valueable today.
For as long as the banker is around and willing to serve the rules respectably your coins would behave the way they aught to.
Grading agencies also keep databases and files and serialises your coin. Meaning they can tell you how many have been graded and where your coin fits in the larger picture.
The true test on weather your grading agency is worth their salt is if an ensurance agency will back them. I don't know how often a coin might need to be re-graded and I think that is another purpose of the seal. Someone can phone in years later and have the agency confirm it's current value based on it's current standing(assuming it's still viable).