sage,
The 'dwarfing' apple rootstocks were seedlings that were selected, at one time or another, for their lack of vigor - often related to the fact that most develop a weak root system. They've been clonally propagated by 'stooling'.
Seedling apples will tend to produce larger, more vigorous, full-sized 'standard' trees, which have largely fallen out of favor, at least here in the US, except in areas of the country that have exceptionally cold, harsh winters which some of the dwarf/semidwarf rootstocks are unable to survive.
Some seedling 'strains',like Antonovka and Ranetka, produce fairly reliable seedling types, but if you're just growing out seedlings from apples purchased at the local market, resulting seedlings could be 'all over the map', with regard to vigor, disease resistance, etc.
If you're determined to grow your own dwarf/semidwarf apple rootstocks, I'd recommend purchasing a few of the appropriate stocks for your site/location, plant them, and create your own 'stooling beds'.

Brilliant. Thank you.