To my knowledge, barley varieties are selected based on agronomics, and kernel fullness/ uniformity.
If anyone wishes to learn more about malting, I recommend the MBAA podcasts by Joe Hertrich. They are not easy-listening; packed with info.
If anyone wishes to learn about barley selection in the US and how barley varieties make it into the AMBA recommended list, reach out to AMBA.
"It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts." - Sherlock Holmes (A. Conan Doyle)
There's generally much more to the malting barley variety selection process such as laboratory analysis, trials, micro-maltings, test mashes, etc... which are measuring the soluble protein content, enzyme levels, extract, diastatic power, etc...
The items mentioned, agronomics and kernel fullness/uniformity alone would be factors in accepting a load of a malting barley variety off the field or from a silo - to be malted, when there is no time for laboratory analysis.
In which case hand evaluation becomes necessary.
Malts and Malting by Briggs et. al. is recommended as a resource for malting knowledge.
Chapter 6.
The selection and purchase of grain.However hand evaluation alone even when carried out by trained and experienced experts, is not enough. Of the grain selected to be top quality at one British site... only 33% malted really well, and no less than 39% was finally rejected.