Then why does there cut sheet say the Voc can be plus or minus 10%, seems like they have an internal conflict.
Not really. All module manufacturers publish a power tolerance range for specific products. For example, REC modules have a positive only power tolerance of 0 to +5 watts (not %). So these are very tight power bins.
Some manufacturers, like REC, provide additional detail beyond power tolerance. In this case, they have stated that the extreme limit of the Voc range is ?10% for a specific module model. They have also stated that the vast majority of modules within a specific bin have a Voc of ?3% of the value on the data sheet. The latter makes sense, given the tight binning.
I suspect that manufacturers publish additional details like Voc tolerance simply due to the increased use of I-V curve tracers in the field. If someone measures 10,000 I-V curve traces in the field, the manufacturer likely doesn't want to get a phone call w/ a warranty claim just because 30 of these modules show a Voc of -10% of the published value.
What manufacturers warranty, after all, is power, which is a product of both voltage and current.