The box said sterling
On this page11
The box was generic and printed
Bought by the hundred with "sterling" already on it, and used for whatever is being sold that month. The statute names boxes, packages, covers and wrappers specifically.
The piece itself was unmarked
Which does not help. The prohibition is on the article OR the tag OR the card OR the label OR the box OR the package OR the cover OR the wrapper.
Two lines shared one box stock
A sterling line and a plated line, same presentation boxes, picked from the same shelf on a busy day. That is how an honest maker ends up on the wrong side of it.
A fineness mark with no qualifier
A plated article may not carry a fineness indication unless accompanied by wording identifying it as rolled gold plate, gold plate, gold electroplate or gold filled.
A quality mark with no trademark
Stamping 14K without also applying a registered or applied-for trademark, or your name. The claim has to have an author.
The trademark was filed late
Thirty days runs from the article being placed in commerce, not from when the paperwork was started.
The clasp did not match the chain
Parts of a multi-part article must carry quality indications matching in pattern and size, in lettering at least as large as the quality mark. Bought-in findings are where this breaks.
The solder pulled the assay
A flooded joint on a small piece, several times over, against a tolerance of three thousandths for the article and seven for the whole thing including solder.
The easy solder was used because it flowed
And it is usually the lowest in fineness. A bench habit with an arithmetic consequence.
The fix is to separate the lines
Different box stock, stored apart, with nothing about metal printed on the generic one. It costs a shelf and it removes the whole category of failure.