An interesting way of thinking.
Surcharge meaning an extra charge over the basic charge is an established meaning with a long history. Originating from France, the word was adopted into the English language. I am not quite sure what makes the heraldic 'charge'
"charge" in the older sense "mark, symbol"
Heraldic terminology is mostly French and not an adoption of French. It does not have widespread use.
A charge is defined as, "anything borne on a coat of arms, whether upon the field ... or upon an ordinary, or indeed upon another charge."
Gough, Henry, and James Parker. A Glossary of Terms Used in Heraldry. (Oxford and London: James Parker & Company, 1894; republished by Gale Research Company, 1966).
Linking the use of surcharge to heraldry requires knowledge of heraldic terms, but ignorance when it comes to the use of that terminology.
This usage is in no way incorrect
'charge' in he meaning assigned to 'surcharge.' Adding 'sur' is superfluous in heraldry. A charge on a charge remains a charge and does not become a 'surcharge.' Also, I am not quite sure how 'charge' translates into 'mark' in the sense of the overprint. This meaning of 'mark' puts the emphasis on it being a symbol, rather than an overprinted value.
If the heraldic use if charge is indeed the origin, below stamps posted by danstamps54 are surcharged.
This being the one example I have never seen referred to as 'surcharged.'