That's pretty high attenuation for that strain (typically 73-77% AA). You're sitting about 10% higher than average. I have noticed higher attenuation on multiple re-generations with this strain, and will typically get higher attenuation with large starters and yeastcakes. These factors coupled with a low mash temperature (what was your mash temp?) and well-managed fermentation temp schedule could push the AA a bit higher than manufacturers suggested range. I would say that if the flavor and aroma is what you expected then you're good. I wouldn't expect a shallow sample to cause an off reading, but you can certainly take another reading at bottling time to compare.