Congrats, and please bear with me, if you will. Your saying and doing a couple things that I think are harmful. Also understand, your gaining success, but please understand, there is no line that determines success. Once you get your charges to reproduce, which is actually very basic. That is merely the begining of "actual" learning and progress. As in, there is a million levels of success. One of the levels is continued success. Also, once you reach success, it reveals more to be successful at. Please keep this one in mind.
First, you appear to be cutting open eggs before they pip on their own. In my opinion, this is a very poor practice. Understand, you can do what you like and most likely you may not do it often. But folks with less understanding then you, will think its a trick that makes you successful and there will be lots of monitors murdered off. Which means, I do not care if you murder your monitors, but please do not teach others to do the same. I think hatching is the first hurdle a monitor must achieve(on its own) If it is too weak to hatch on its own, then in all likelyhood, its too weak to live.(but thats ONLY my opinion) In other words, I don't think its a good idea to be shipping people monitors, that could not hatch on their own.
Second your nesting box thing. That is without question hard on females. Heres the point, if you can see the eggs being laid(take a pic) then the female is suffering. As in, thats a nasty poor thing to be doing and allow to be done.
Of course you can do it, and you can do it a few times. But again your teaching the worse way to accomplish a task not one of the better ways. As an example, You recieved how many clutches from a single female in this manner?? under five, and you mentioned you retired the female, maybe ten? Now compare that to some monitors that have "better" nesting choices. I have a female thats laid 65 clutches and is still going. Or a female ackie that has laid 17 in a row and is still going. All our females lay four or more clutches a year, year after year. Yes, my method is more work(at first). But what else are you going to do with yourself, make the monitors do the work and suffer the effects.
Heres the reality, and you will indeed face this reality. Heck I am sure you already have, to a small point. There are a million methods that can work. Some of those methods are critical, that is, you have to have the conditions exactly right and keep it right. Nest box type nesting is OK, for a clutch or so(bragging rights) but Nest boxes require constant maintenance and more importantly timely maintenance. If you set up a nest box at the time it SHOULD be set up, then its dried out by the time the monitor is ready. They SHOULD be set up at the time of copulation. Not at the time the female is past due. Causing females to carry eggs past when they are due, is not a good thing, just ask your wife, or a friends wife if they would like to commonly and needlessly carry PAST DUE. They will most likely not answer, but instead hit you with a pan or something that will leave a mark.
As you know, I support large nesting areas, I support that with all types of reptiles. For me, it makes something difficult into something easy. Then consider, something easy will be much easier to do over the "long term" heck, its even better in the short term(for the female monitor)
Heres the deal, doing everything for the animals is narcissistic(all about the person) and being is we are people, its very easy to do and of course very common. The cool thing is, monitors know how and are very willing to do all this stuff on their own. They will dig their own burrows, pick the right temps, make their own nests, heck even hatch their own eggs. All they need is the stuff. Give them the stuff and sit back and enjoy watching them do what they do.
All this leads to the point, Humans make mistakes, it appears we are designed to make mistakes. So take the possibility to make mistakes out of our hands. Put those tasks in the hands(claws) of the real experts, the monitors, WITHOUT question, they were designed to make those decisions and have done so, since before man was man(monkeys). The key is, its easy to do and once you do it, its far easier then doing all that work monitors WANT to do.
You may someday understand, the reason everyone else falls out of breeding monitors is, they make it toooooo much work. They get tired of making mistakes. I make it easy(again narcissistic) If its easy, then both the monitors and I will continue to do it. If its hard, we both(the monitors and I) will most likely quit.
Also, saying a substrate is good because it holds a burrow is very very very very naive. There are something like 4000 types of dirt, nearly all of them hold a burrow, monitors use only a small percentage of those 4000 kinds. Which means, there are other reasons then it holds a burrow.
With that in mind(quit) I will take leave, again congrats and keep on progressing. Cheers