Also, remember that an e-ticket receipt issued by a US carrier must by law show you the baggage charges for each of the first two bags as well as other pertinent limits such as weight. This is shown segment-by-segment.

What shows on your e-ticket is what the check-in agent will see when you drop your bags off. Thus, you will always know your allowance and if it appears to be wrong, you may call in before you travel rather than having a dispute at the counter.