there's no requirement the company is listed on the stock exchange. The requirement is a letter of financial audit stating the corp revenue is a minimum of $50 million.
I'm doing the Work Professional LTR. The only difference from the DTV is the corp financial audit documentation and the $50 mill/year corp revenue requirement.
For those interested in applying for the DTV as an employee of an offshore, non-Thai company all of the documentation is very simple. I spent a few hours gathering the required information and submitting it to the Thai embassy in Washington DC. Approval took a few weeks. It's very straightforward. No need to waste your money on a third party. However I'm considering switching to the 10 year "Work from Thailand Professional" LTR visa. The requirements are quite similar but the benefits seem to be much better.
MTL or Thai Life. Both are highly recommended by the doctors and nurses that I spoke with while in the hospital. No issues with unexpected refusal to pay issues leaving you with major expenses draining your bank account.
I believe there was a 1 week delay when Thailand announced a clarification to the requirements, otherwise, it probably would have been 2 weeks like others experience before I submitted an application.