The issue of audience measurement discrepancies has long plagued online publishers. While most have made peace between their internal numbers and the usually lower ones reported by Nielsen and comScore (NSDQ: SCOR), NYT reports that in the case of Hulu, the wildly divergent figures appear to be more vexing than usual for both Hulu and advertisers alike.

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The March tallies from Nielsen say that the video site received 8.9 million uniques that month, while comScore reported 42 million for the same period. Apart from those inconsistent counts, things only get more confusing in April. According to Nielsen, last month, Hulu served up 373 million video streams, charting a steady growth trend from March’s 348 million and February’s 309 million. At the same time, Nielsen claims that Hulu is seeing declining numbers of unique visitors month to month: in February, the audience measurement firm says Hulu had 9.5 million visitors in February. As for April, Hulu attracted just 7.4 million uniques, as per Nielsen. Meanwhile, another online measurement provider, Quantcast, has found no evidence of an audience decline at Hulu.

Of the Nielsen problems, Hulu diplomatically says “there is work to be done.” To some media buyers though, it only shows that measuring online video views is still an unreliable science. In addition to affecting advertising decisions, more months of declining traffic could make content companies more reluctant to place their videos on Hulu, though that didn’t seem to stop Disney from finally deciding to sign a deal that brings shows from the ABC broadcasting network, along with some cable channels, over to Hulu last month. But it could give CBS (NYSE: CBS), now one of the last major holdouts from the NBC Universal/NewsCorp. JV, another reason to keep its distance.