Can I still use BullseyeBore Core for drill alignment if only a portion of the patterns are visible on the worksurface?

Yes, typically as long as 50% of the Reference Pattern and 50% of at least one of the corresponding Alignment Patterns are visible, BullseyeBore Core can be used for drill alignment. This can occur when drilling near the edge of a worksurface or near the corner of a worksurface. Here is a video that demonstrates edge drilling.