Here is ETIQUETTE VIGNETTE NUMBER FIVE – Agreement on Results of Play (refs: Law 65C and 65D.)
a. “Quitted” (played) cards are to be arranged in an orderly, overlapping row in the sequence played…” (part of Law 65C)
b. “A player should not disturb the order of his played cards until agreement has been reached on the number of tricks won”. (Law 65D; emphasis mine)
c. The hand is over; you quickly fold your cards saying, “Bid three; made four”. There is NO agreement that you are correct. An opponent objects, “No, you bid four and made three”.
d. “A player who fails to comply with the provisions of this Law jeopardizes his right to claim ownership of doubtful tricks or to claim (or deny) a revoke.” (Law 65D continued)
e. Hopefully, your partner did not follow your mistake. Otherwise your side “jeopardizes” its ability to prove to the Director that indeed you did make four after bidding three.
f. Result if the Director agrees with your opponents that you bid four and made three?
1) One example:
a) Three NT making four (non-vulnerable) = 430 for your side
b) Four NT making three (non-vulnerable) = -50 for their side.
In short: 1) know when to fold; 2) which is after agreement is reached on tricks won; 3) if your partner folds before that, you should not.