The browser interface of the object tool etc allows the library person (me) to gracefully deprecate old objects, and steer users toward the good ones.
When we update an object, we move the old one to the xOld R&D folder. This folder loads, so placed instances of old objects will continue to work. The updated one is the only one visible in the proper folder, so there's no question about which one is right. There's a Center Line symbol, it's in Graphic Symbols, and that's it.
Can't do it with markers. The marker chooser makes things more confusing than they need to be. For example, on the detail marker list, three out of thirteen items are meant to be used.