It's a mather of opinion i guess
i always pull back as much as possible. Maybe i overdo, still to each his own.
Once i drew back (bi-shot) and saw nothing. Then did it again with more force and one drop of blood showed up in the yellow cap (30 gauges are yellow). So i was not in a main vein and it probably meant nothing, but i pulled out and started again. I like a clean job done.
But as said, this was nothing to worry about, i think.
Jeff