Acrobat Overprint Preview is innaccurate

[defaultrjaomfiv0pg5]

I've just done an overprint check after some errors came back from the printer. We're able to see some text on a dark background does get printed over when we turn on Overprint Preview in InDesign but this doesn't seem to be the case with the PDF the printer sent back to us that they used.

I've tried a few other test runs with different documents but the Overprint Preview in the latest version of Acrobat seemingly doesn't work at all.