Well I have to say I agree with you BUT I also see the flip side of the coin. In the U.S.A. there are so many laws on the book and insurance reasons parts cant be made to fit perfectly. Patten laws for example make it hard to make parts fit perfect.
Here is an example, Lets just say you start making and selling grill guard for the 4020 and it fits like a glove, I mean perfect. You have taken the time to make sure that it fits lets say 100 different 4020 so you can say its an exact fit. You sell 1000 of them and make $40 each profit. Now Mother Deere finds out what you are doing and says OH NO YOU DONT! They slap a big law suite on you and covers you up in legal costs and shuts you down. In the end the judge tells you if did not make a perfect copy of Deeres part you would not have had these problems and wouldn't be broke now. This is why aftermarket parts don't fit perfect, They have to be made just enough off to keep them out of trouble and still be able to make and sell parts.
It aint right but that's just the way it is now a days. I myself have to use aftermarket parts to make it and get by because I am not a BTO with deep pockets. If you want perfect fitting parts buy OEM parts and be done with it.
I really do get tired of people trashing aftermarket parts "That they AINT good enough". They can not be made the same as OEM for legal reasons that's why they have to be made off a little. I am sure that they get plenty of calls from guys just like you complaining about the fit every day, And the funny thing is they can not do anything about it but take it because its the only way that they can make the part and sell it.
So you can spend the big bucks and buy OEM and get the perfect fit, Or buy aftermarket a lot cheeper and make it work and be done with it. Its up to you! Bandit