Based on the easily proven temperature dependency of the OLR, there is no reason to believe that the difference is satellite calibration error (although that doesn't mean there is none). (theinconvenientskeptic.com)
It also doesn't exhibit variation of calibration error with age, but such variation shouldn't have a significant impact unless, over the range where the likelihood function for the sample is significant, it is substantial in relation to 14C determination error. (climateaudit.org)
In other fields, these kinds of issues arise in unacknowledged laboratory effects or instrument calibration errors. (realclimate.org)