I emailed someone about some Cinelli handlebars he was offering for sale to find out what clamp diameter they were, and he says they are 26.2. I can't find any info about 26.2 stems or bars and I am wondering if these really exist. I know that a lot of vintage Cinelli bars had 26.4 diameter, and some had 26.0, but I wasn't aware that they also came in 26.2? Is it safe to assume that these are 26.4 and it is just a mis-measure, since .2mm is pretty easy to miss with most calipers?

it is safe to assume they are 26.4. In fact ALL cinelli bars and stem were 26.4 until the early 1990s.