Regarding Excalibur/Krypton chess computers having the same program: Excalibur Legend II is obviously a clone of Sphinx Legend II, Avenger is a clone of Krypon Comet.

Igor, Ivan, Mirage, are Ron Nelson programs, not by Gyula Horváth. I know there was speculation about it in the past, but I thought that was cleared up after Ron Nelson posted on a forum and told about his work at Fidelity and Excalibur. In the first year or two at Excalibur, their chess computers were manufactured in Eric White's factory, so from the outside they look similar to CXG/Krypton ones. Even the LCD is the same. The chess program is different.

If there still is/was any doubt (like thinking that maybe Ron Nelson subcontracted parts of the program), now that there are ROM dumps available, people that want to check more thoroughly can do so by comparing/examining the files or parsing them through a disassembler or MAME's debugger.