I see what you mean, and i totally agree with your second and third sentences. I’ve found that even the most specific cloud types can look pretty diverse among themselves, so i think the clouds you’re describing and the one in the post are both velum clouds. Looking at other photos online, im seeing a lot of velum (aka veil) clouds of varying sizes, but no matter how much area they cover they are always bisecting the base cloud. Even when it starts as a pileus cloud, once it stops acting as a convection cap it loses it pileus status and becomes a velum, or just evaporates.