All kings of Israel were suppose to write down the law themselves (I guess that's should cover the printing press thing) so each king would know what the law was and have his own copy. Besides there was an entire priesthood that the king could have counted on to know exactly where to go for any questions. Herod's real crime was he sought his own glory and didn't obey the very first of the 10 commandments.
The Egyptians were given ample chances to release the Hebrews. Let's not forget that the only reason why they survived the 7 years of famine were because Joseph (a Hebrew) could tell Pharaoh what his dream was and what it meant. (Oh and it was every first born that was killed, not just children.)