Not necessarily true, my 1 yr old BO with a 14 week "new" additionThis does not answer your actual question but if I was in the shoes I think you’re in from reading your post, I would want to know that 6 week old pullets have a long time yet before they are of laying age. In my experience the flock never really accepts newcomers until they start laying. They will need spaces to hide and escape the other adults should any be inclined to be hostile. Which you could bet money at least one will.
People have varying opinions on space, and you will have to ask yourself what your goals are. Do you want a happy peaceful flock with low stress for the birds and for yourself? If you do then 10x10 for these pullets all by themselves would be pushing that. The minimum space requirement quoted often here are minimums for factory farms, many if not all are only able to stock so many birds together by buying debeaked chicks to avoid bloodbaths.
Good luck with your flock and I apologize for cluttering up your thread not answering your actual question!