Daniel, formally you are right. Nothing in the Spanish text specifies if the King could leap while in check, nor if he could fly over threatened squares (at Grant Acedrex). However, it can be extrapolated that it was the case by comparison with the rules played at (standard) lepchess as reported in other contemporary sources.
Allowing that King's jump to escape a check would be anachronistic in my opinion.
Daniel, formally you are right. Nothing in the Spanish text specifies if the King could leap while in check, nor if he could fly over threatened squares (at Grant Acedrex). However, it can be extrapolated that it was the case by comparison with the rules played at (standard) lepchess as reported in other contemporary sources. Allowing that King's jump to escape a check would be anachronistic in my opinion.