Nbu Or PL

Technically they're different but they are frequently used interchangeably as in this case. Up to and including '67 they were PL. '68 and later are BU but it took until around 1980 before ICCS changed. And then they changed to NBU. Charlton calls them MS NC (non-circulating) to add further confusion. And then in 2004 the RCM started putting circulation coins into some sets. 2010 is the year the last BU coins were struck.

Hard to tell for sure unless you know the source and look it up in Charlton Vol 2. Some years they even put specimen coins in the pliofilm sets instead of BU. It's basically a matter of training your eye by comparing high grade circulation coins to ones you know are BU. The BU ones are kind of shinier and 'cleaner'. Due to the steep price differential; when in doubt assume BU for a sharp looking coin unless it's in a reliable TPG's holder identified as circulation. For older years a rule of thumb is that if you can see your fingernail reflected on the coin then it's most likely (although not guaranteed) to be PL/BU. Starting in 2004 though that no longer applies of course.