I'm working my way through the revised edition of Robinson and Pierpont (I'll give a full report when I get to the end) and am coming across cases where arguably what is printed is less smooth than what is found outside the Byzantine tradition. In Mark 13:31 Robinson and Pierpont print Ο ουρανος και η γη παρελευσεται using a singular verb for a compound object. They note marginally the Byzantine variant παρελευσονται, which is of course the reading of enough of the textual tradition for NA27 not even to note the variant.
I have two questions: (a) is what Robinson and Pierpont print indeed less smooth? (b) if so, are there other cases where less smooth readings within the Byzantine tradition are not noted in critical editions?