From Darcy:
« you must try 3 times in a row, if you pass a shinsa year you will have to queue up again from scratch ». Guido stated in a post he had a sword which passed on the second try.
Needless to say that Darcy’s posts are based on two decades at least of top blades ceaseless hard studying.
That is why it is difficult for most of us to really understand Nihonto, you must spend years to exercise your eyes on the best swords, difficult when one is on a limited budget.
The rest is hours of studying the why’s of the shinsa, for this you must have done what is written in the precedent paragraph.
Remember Sherlock Holmes (nothing new under the sun), I try to quote:
« If you know by heart the details of one thousand crimes, it will be easy to solve the following one ».