IMO this remains unclear. To try to create a timeline, I'd start with this article by Ed Zollars:

https://www.edzollars.com/SelfEmployedHealthInsurance.pdf

It cites a CCM also issued in 2005, which doesn't help us too much but does clearly open the door to individual policies and not just policies established in the name of the business. But Ed does a great job of identifying the "problems" starting at the bottom of page 3. We have nothing new from Congress and not much from the IRS to help us with these problems.

The next "get off the bus and look around" stop on our historical tour of SEHI takes us to a CCM written in 2012:

https://www.irs.gov/pub/irs-wd/1228037.pdf

If you thought the rules at least made some sense prior to 2010, this about-face was a real head-scratcher. As indicated in the last substantive paragraph of the document, the change to allow Medicare premiums as SEHI came about quietly when someone at the IRS decided to rewrite the instructions to the 1040, beginning with tax year 2010.

I've seen arguments online that take the position that the Sch C business have a "plan" to pay for the owner's (and spouse's and dependents') health insurance costs. "Look, now we have established a health care plan!" Ed points out that this plan need not be in writing. It's unclear to me whether this approach will fly when it comes to retiree coverage (or union coverage, which I've also seen). Prior to the change to the 2010 instructions I would have fairly confidently said "No, that's not SEHI." But then when they said that Medicare is allowed, who knows what else might be?

This thread started out with a focus on the word "subsidized" but I think the real crux of the problem is the undefined term "by any employer". Current? Former? <shrug> The lack of Tax Court guidance suggests that maybe the IRS is choosing not to litigate these cases.  Ed makes good arguments in both directions that I think are just as good today as they were nearly 20 years ago.

IMO, this comes down to what position is your client comfortable taking, what position are you comfortable taking, and what disclosures may be required based on your analysis of the probability of success if challenged.

Are we having fun yet?  I just finished a 3-day IRS Nationwide Tax Forum so I know I am!

Rick