I don't think there is an industry yardstick anymore in regards to lbs of hops per barrel. There are so many hop varieties used today, with an insane array of alpha acids (from as low as 2-3% to 20%), and a limitless way to add hops to beers today (mash hops, fwh, bittering, finishing, hopback, dryhop, etc), it's virtually impossible to come to any sort of average.
And knowing that DFH 60 claims to be 60 IBUs is of little help. I wouldn't be surprised if DFH actually has had the IBU level tested, as they are big enough to do so. But another brewery, who doesn't have their beer tested, could also claim to have 60 IBUs, when it may actually be 40 or 80 or 60. THERE IS NO WAY TO KNOW.
And what does 60 IBU tell you? Nothing, it's just a statistic. Yeast, malt and water are just as important when determining how "bitter" a beer is.
For example: attenuation rates. I was looking at recipe stats for some historical imperial stouts, and the amount of hops used equated to something in the neighbourhood of 200 IBUs (calculated). But the average attenuation was only around 60%, and these beers were typically aged before selling, so the end result was likely nowhere close to as bitter as the IBUs would lead you to believe.
Don't get me wrong, I love learning about historical beers, and how commercial beers are made today. However, there are so many "non-measurable" intangibles that play a role in the finished product of a beer which statistics simply cannot account for.