Just a few thoughts and ramblings from a non - expert. I am sure the Barn will correct me where needed
My opinion is we are dealing with designs, materials, methods from the 20s and 30s. Can't expect anything close to perfection. Even in today's world we have warranties on new because things happen.
How much of this is due to the age of the design - materials, design tools, etc.?
In the day, I wonder what Fords scrap rate was, probably a lot higher?
I wonder what the rework rate was, a lot higher?
Is inspecting/grinding heads a science, or more of an art? I do not know, seems to be a lot of discussion on what is proper once you deviate methods for the customer/mechanic. Sounds like Berts has the proper equipment.
How many vehicles had Warranty issues with blown gaskets, warped heads?
If the issue is with the castings, or with material - with the volumes being so low, foundry might not care, and Bert's is too small to sink money into research.
Berts can not control environmental stressors once it leaves Berts - Temp fluctuations, Humidity, stresses in shipping, and what happens at the customer. So heads may ship OK, and have issues at install. This is my opinion.
Are new Heads seasoned, do not know, have been told it is better to use good original parts because they have been seasoned and are more stable.
A part as large and heavy as the A head seems to be a stable metal part, and the assumption is it will never change form - not true, temp change and other factors causes it to change.
In the day the part was designed without computer tools, no ability to look where metal and temp stresses are in the head and design for them. If designed today the head metal/material would probably different/modified, and shaped differently to deal with stresses.
In Berts defense, I myself have been guilty of blaming a supplier or product for something and been wrong. After cooling down and working through things with the supplier find that it is me either doing something incorrectly, not ordering the best quality part (guilty of trying to save dollars, ends up costing me a lot more), or not understanding something. If a supplier is willing to work with you they are usually reputable, and want to see happy customers, if not they will not be in business long.
Of course stuff made in China, South America, etc., bought on the internet, not from a reputable supplier is a different subject.