Not sure about this question. Let's say you have the genotype (genetic code carried in the vegetatively propagated plant) and phenotype (the expression of the genotype in terms of looks, taste, etc.). With garlic it is well known that growing conditions have an effect on phenotype/expression, but except for a few obscure Asian strains, it is considered sexually sterile.

Until scientists started messing with GMO garlic, genotypes were stable for hundreds or thousands of years, or so they say.

I recently read two garlic books from the library so I hope I remember them and the info correctly.

I think it was Ron L. Engeland's Growing Great Garlic book that mentioned watching for "off" types when separating heads into cloves for planting. He was of the opinion that these different bulbs should not be included in the planting stock for that variety, but might be possible sources of new varieties. This sounded like his opinion, not a genetic analysis. Yet his opinion may have some merit as many consider his book THE DEFINITIVE ONE for garlic info. And he certainly has grown and studied LOTS of garlic at Filaree Garlic Farm.

I'm wondering if the genetics could alter in a single clove which then gets planted and produces an "off" type bulb....much like a sport on a tree or shrub branch. If so, that could be grown for a new type, unless the sport is unstable. I don't know the genetics of sports in trees and shrubs, much less in garlic.

The other book I read told of how to manipulate scapes and get true flowers in garlic that then produce true seeds, not bulbils. This would result in new genetics in the seed which would take several years to grow out into a full size bulb. Producing seed is an involved process and doesn't work for all varieties, not even all hardneck varieties. Again, if I remember correctly, it's in The Complete Book of Garlic: A Guide for Gardeners, Growers, and Serious Cooks by Ted Jordan Meredith.The book is beautiful just to look at and is even better if you like growing garlic. Qualifies as a coffee table book in my opinion, except my tables are covered with too many other things.

We have a library system that works great for requesting books on loan from other branches in the system. It's a great way to take a look at books I wouldn't buy myself without more info. I ended up taking quick looks at several other library garlic books that I didn't care for at all. Felt kinda bad someone had to find them and send them across the county so I could look at them for 5 minutes :(

Hopefully, I've remembered the great garlic books correctly and the info they had in them.

So many generations of clones and lack of genetic diversity make it unlikely garlic alters genetically. I think many of the varieties we have named are repeats of each other. But nature loves diversity and it is possible to see sports in garlic like any other plant. We now have pink daffodils after all.
Have you done any actual seed saving? I know some people online doing some garlic landrace breeding with seeds.

Garlic will mutate just like any other thing grown from genes and chromosomes. You tell by the appearance of an off type, that comes back true to be most likely a mutation, since all its offspring are clones, and should be identical to it. .

In vegetatively propagated plants like garlic, the mutation will not be in the germ cells but only in one part of the parent plant and what gets descended from it. The initial appearance most likely will be perhaps a single part of a clove or so and if that then it may need a number of generations to build a whole plant with the mutated genotype in all its parts.

Complication with garlic is that expression can be quite different under different conditions without any genetic change. However any specific type that stands out from its fellows is always a candidate to be selected for special consideration. You propagate from superior stock just like you cull out the inferior. It always pays to run some years of testing, however, so that any new and improved type does not have a fatal Achilles heel in the process.

Mutations are normally not viable anyway, and those that may be are usually inferior to established types. Those rare exceptions to those limitations have always been the basis for new varieties.