Agreed with above.. perfectly fine.. actually the best way for you to get a consistent harvest.. If you take the whole plant it will be more imature as you go down.. unless you have a crazy light setup or your outdoors.. and even then same idea just not as drastic..
just ask yourself... when tomatos, cucs, roses, etc... are ready do you chop the whole plant?? or pick as they ripen/bloom???
Same idea.. the plant sections mature at different times.. especially with weaker lights that don't have good canopy penetration..