Hi Uncle Donald,
With 10-14" hair length the weight of the hair tends to pull the hair straight. The longer the hair the more weight to 'pull the curl out.' I'm sorry but I'm not aware of any product that will restore the curl but maybe some other readers can make a recommendation. I don't think a flatback ventilation will help much as it's the natural aging of hair. We can do the shorter style with fallback ventilation--no problem. With the shorter style the curl will last longer.
Regards,
John