Two weeks ago Ad Age issued a report that showed Samsung topping the list of the 10 fastest-growing ad spenders in the U.S., with total ad spending up 58% year over year.

Apple’s (AAPL) growth in ad spending didn’t make the top-10 cut.

Apple did make the cut in the chart Ad Age issued Monday of America’s 25 most-advertised brands. Cupertino came in 12th in the new chart, with ad spending up 21% year over year.

Samsung, whose spending was reportedly up 125% year over year, came in two spots behind Apple at No. 15.

That’s a little surprising, given that Ad Age reported two weeks ago that Samsung’s $4.3 billion worldwide ad budget in 2012 was four times bigger than Apple’s.

Moreover, how can Samsung’s ad spending be up 125% this week when two weeks ago it was up only 58%?

The answer to the second question may be in Ad Age’s fine print.

Monday’s report covered so-called “measured media,” which includes spending on TV, radio, print, outdoor and Internet display ads. The report two weeks ago also covered “unmeasured media,” an advertising term of art that includes Internet search, shelf placement, coupons, events and in-store promotions.

But that still leaves the mystery of how Samsung’s advertising department can outspend Apple worldwide by $3.2 billion, yet underspend Apple in the U.S. by $65 million.

Any theories?