I would like to create an style-unified collection of cartographic symbols - mainly for use with free SW like QGIS.
Am I right if I think that I can freely mix and modify distributed content without need to cite sources for particular icons? I plan to keep the CC0 1.0 Universal (CC0 1.0) Public Domain Dedication license even for my original additional icons to not to restrict use in any way and I plan to add something like "Some icons are from source 1), some from source 2)" etc. - just to be fair.
Is it OK?