Something fishy about this Pompeii story

This is one doofy story:

Remains of rotten fish entrails have helped establish the precise dating of Pompeii's destruction, according to Italian researchers who have analyzed the town's last batch of garum, a pungent, fish-based seasoning.

OK, so far so good. But wait a minute! We have a perfectly good historical date from Pliny the Younger! August 24, 79 AD. There's not any chance that some kind of radiometric date is going to improve on that. So what's the deal?

Doubts about the date of the eruption emerged a couple of years ago when archaeologists discovered a coin which seemed to refer to the 15th imperiatorial acclamation of Titus, believed to have occurred on Sept. 7, 79 A.D.

OK, so the coin supposedly was later than the eruption, even though it was in the site. But wouldn't the simple explanation be that they struck the coins in advance of the event? Well, I guess there's also this:

"Unfortunately, that coin can't be taken as a dating evidence, since it is hardly readable. I myself agree with Ciarallo's dating of the eruption, even though I think that a bit of mystery remains. However, it is not so important whether the eruption occurred in August or in October," Teresa Giove, a coin expert at Naples' Archaeological Museum, told Discovery News.

So where does the fish sauce fit in?

"Pompeii's last batch of garum [fish sauce] was made with bougues, a fish that was cheap and easy to find on the market in those summer months. Still today, people living in this region make a modern version of garum, called "colatura di alici" or anchovy juice, in July when this fish abounds on the markets," Ciarallo said.
The eruption froze the sauce right at the moment when the fish was left to macerate. No batches of finished garum were found, since the liquid evaporated in the heat from the eruption.
"Since bogues abounded in July and early August and ancient Roman recipes recommend leaving the fish to macerate for no longer than a month, we can say that the eruption occurred in late August-early September, a date which is totally compatible with Pliny's account," Ciarallo said.

OK, so they don't keep the sauce macerating for more than a month. And September 7 is...less than a month after early August. Uhh...what was the story here? Why were we doubting Pliny again? I mean, I admire the knowledge that goes into this, and it's pretty cool to analyze ancient fish sauce, but this story just wasted my time!