Other mistake: When YoYo drops Herman after the potion wears off, his wig flops up.
Other mistake: Herman's Dr.'s appointment is at 9am but the wall clock in the Dr.'s office shows the time at 9:33 or so.
Suggested correction: Most doctors keep patients waiting much longer than this. The clock should have read 9:45 at least.
Come Back, Little Googie - S1-E25
Other mistake: When Eddie's naughty little friend goes to shake hands with Herman they insert a quick close up of a hand buzzer in his hand, only it's obviously an adult's wrinkly hand.
Herman, the Master Spy - S2-E2
Other mistake: The Russian trawler shown appears a lot closer than three miles out. At that distance from the beach it would be very small in size, if visible at all, and then only if an observer had binoculars or telescope.