This was my path, so it's possible. I dropped out after year two of my degree to join a startup and worked for 10 years in industry.

I converted 8 years of that experience to 2 years of a bachelor's degree to make the full 4 required, and had a University professor provide a letter of endorsement.

I was applying from Europe, and even then it was apparently a fairly expensive process for my sponsor.

Absolutely correct. The requirement is a four-year U.S. bachelor's degree or it's equivalent which can be a foreign degree or a combination of education and experience (or even just experience) evaluated to be the equivalent of a U.S. bachelor's degree. The rule of thumb is that 3 years of professional experience is the equivalent of 1 year of college education.

Thanks for the clear answer! is proving the years of experience usually difficult? e.g. references from 12 years ago can be hard to get (although I have those 11 years ago myself).

Not at all. Detailed prior employment letters are enough.

> The rule of thumb is that 3 years of professional experience is the equivalent of 1 year of college education.

I know you don't make the rules, but on the surface it would seem that these numbers are switched around ;-)

You're probably right!