when they were finalized. The Q source was written during or shortly after Jesus' life. The author of Luke even admits his writing is a compilation from multiple sources in the beginning verses.
Second crucifixion was more broadly applied than just crimes against the state. If a slave killed his Master, under Roman law, all of that master's slaves were to be crucified. Tacitus documents a case of this where the Senate tried to stop a crucifixion of 400 slaves. Read it for yourself.
https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Tacitus/Annals/14C*.html