One thing you have forgotten is that most of a clan's tattoos would be done by one tattoo artist and his/hers assistant. This person would be skilled in applying the tattoos quickly and within the confines of the ritual involved. The tattoos artistic style will be the same for everybody within the clan with similar designs used. Also if you are going to be marking your skin for life you would want to have a well drawn tattoo not some poorly scribbled scar or ink blob.
Cheers Darran.