Scotland really is a seperate country within the UK
(I am not pointing out that it should be changed but I genuinely want to know)
If an eastern Moldovan insisted that their country was "Transnistria", would we respect that in the same way? Or Chechnya, etc.
Having said that, we can use the term "country" a bit loosely, so there doesn't need to be a big debate about it.
Vermont is trickier, but I would still say they qualify as independent as they were definitely a sovereign state, and they had full control of their territory.
What I will say is that I think Texas's borders should be reduced to what they actually controlled, which was a much smaller part entirely within Texas's modern borders.
I think that Texas was a “country” for 10 years during the 19th century as much as Crimea was a “country” for a couple of days in 2014: both had control of its territories and were recognized by a major power. But the end-game for both so-called republics was to be annexed by the big neighbor next door.