Entries get filed under time pressure, with invoices that arrive late and classifications that turn out to be wrong. The post summary correction, PSC, is the formal way to fix entry summary data after filing and before liquidation. It is not a loophole and it is not unlimited. Used early and honestly, it is how reasonable care looks in practice.
What a PSC can and cannot change
A PSC can correct most data transmitted on the entry summary: value, classification, quantity, origin, and many duty and fee calculations, as long as the entry has not liquidated. It is filed through the automated system and replaces the earlier summary data for that entry, creating a clear record of what changed and when.
Some things sit outside it. Liquidated entries need a protest or another post liquidation tool, not a PSC. Certain corrections that customs treats as claims, such as some preference or drawback related changes, follow their own routes. The broker's first question on any error should be timing: has this entry liquidated yet, and if not, how long is left.
Timing is the whole game
Liquidation normally happens months after entry, which gives a PSC window, but that window is not a reason to sit on a known error. Customs can liquidate early, and an importer who finds a valuation error in week two and files the correction in month nine has a weaker story than one who filed in week three, even if both corrections are technically timely.
Build the discovery into normal work. A monthly review that samples recent summaries against commercial invoices will surface the transposed digit, the wrong currency conversion, and the assists that never made it onto the value line while every one of them is still correctable by PSC.
Duty going up versus duty going down
Corrections that increase duty owed are straightforward in spirit: customs wants the money, and paying it voluntarily with interest is the clean outcome. Corrections that decrease duty get closer reading, because the importer is asking for money back, and the supporting documents need to prove the original figure was wrong, not merely less convenient.
Keep both kinds in the same file discipline. The invoice, the worksheet, and the reason for the change should be attached to the correction record whether the adjustment favours you or the government. Selective paperwork is the fastest way to turn a routine correction into a focused review.
When the error is a pattern, not a typo
One PSC is maintenance. The same correction on forty entries is a disclosure problem. If a review finds a systematic error, a wrong classification used for a season, a valuation method applied backwards, the right move is to talk to counsel about a prior disclosure before customs finds the pattern itself. Voluntary disclosure changes the penalty conversation completely.
Do not let the ease of filing a PSC hide that choice. Correct the entries you can, quantify the ones you cannot, and make the disclosure decision on the full number, not entry by entry.
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Frequently asked questions
What is a post summary correction?
It is an electronic amendment to an entry summary filed before that entry liquidates. It can change value, classification, quantity, origin, and related duty calculations, and it creates a dated record of the correction.
Can I file a PSC after liquidation?
No. Once an entry has liquidated, corrections go through protest or other post liquidation mechanisms, each with its own deadline. That deadline pressure is why known errors should be corrected as soon as they are found.
Does filing a PSC trigger an audit?
A single, well documented correction is routine and is generally read as reasonable care. Repeated corrections pointing at the same underlying error are different, and can invite questions about the system that produced them.
What if my correction shows I owe more duty?
File it and pay the additional duty with any interest due. Voluntarily correcting an underpayment is materially better, in penalty terms, than having customs find the same error in review.