There are some 80-90 million SWF files from the last eleven years and in ten versions scattered across the web. Versions 7 to 9 are all still widely used on popular websites. Version 6 is quite common, and even versions 4 and 5 are still found - largely for classic games or applications, but sometimes in new files generated by alternative SWF compilers. (The openoffice.org SWF export still uses version 4, though it produces poorly formed SWFs).
It's quite unusual to find any use of __resolve in real Flash movies. That's why it hasn't been supported in Gnash up to now. But after investigating why Gnash didn't play the Flickr widget, it turned out the widget relies on __resolve to implement certain functions of the Flickr API.