Like you said, once you see everything happen the first time it gets alot easier and you know what to look for. As far as missing a prelay shed, those girls are the exceptions, I have yet to have a girl not have a pre lay shed. Also, if you look at your girl every day its almost impossible to miss an ovy. I can tell days before mine actually ovy, then it looks like they ate a football and are going to pop. Ovies can last for days so you shouldnt miss it. In addition a female that is about to lay should be massive, sitting on the hotspot constantly in a perfect coil and will start laying inverted and contorted in the weeks leading up to laying while they are trying to position their eggs for laying and will get what some people call "puff butt" where their is a bulge near their cloaca a day or two before actually laying.