Short measure
Updated
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The conversion mistake
A 236 ml jar is sold as 8 fl oz, 8 becomes the number everyone remembers, and it goes on the label as 8 oz by weight. Wax is about nine tenths the density of water, so the jar holds closer to 7 oz and the label overstates it.
The fill-height mistake
Capacity is brimful. Nobody fills a melt cup brimful, so even a correct density conversion against the catalog figure overstates what is actually in there. Only a weighed fill answers this.
The formula change nobody carried through
A new wax or a higher fragrance load moves the weight, and the label stays as printed because labels are ordered in quantity. That is the version of this failure that survives longest.
What the rule permits, and what it does not
500.25 allows variation from ordinary exposure in good distribution practice and from unavoidable deviations in good packaging practice. It does not permit an average that falls below the stated quantity because the figure was estimated.
Averages are what get checked
The permitted variations are framed around the average of the quantities in a lot, so a process centered exactly on the declared weight will fail half the time. Centering slightly above it is the ordinary answer.
Weigh a sample from every run
A few units off each batch, recorded with the date and the batch. That is the whole control, it takes a minute, and it is the only thing that makes the declared figure defensible later.
Centering and variation are two separate decisions
Where you aim the fill and how tightly you hold it are different questions, and a loose process needs more headroom above the declared weight than a tight one. Weighing a sample from each run is what tells you which you have.