Silver/gold coins, value below that of metal

Sometimes there are coins that are valued less than their value given by the metal.
We all know that gold and silver rise and fall.
So sometimes purchase values ​​are entered that are not in line with the market trend.
In this case the value of the coin is estimated at 4 euros.
But the value of the metal is 4.85. In my opinion, it would be correct if a system was inserted that automatically updates the values ​​of the coins when the cost of the metal increases.
In this case the 4 euros should be replaced by 4.85.
It would be more correct.

the easiest way to have the value as BV, which is linked to bullion value
a coin in F condition isnt worth more than that

This is on the to do list already :)

Best way for bullion coin pricing is using margin, if i bought 1 oz gold coin 5 years ago for 1000 eur it was +7% to spot exchange price.

Now spot price is 1360 eur and numista calculation of value is not correct.
if you add one more field for gold coins - "spot margin" - users can put there information and you can recalculate price
fox example today spot +7% will be 1455 eur (not 1000 like now)

P.S. or instead of margin, we can use date of purchase, so server can calculate margin from gold historical prices.