I have a 50/1.8 Mk 1 with a date code UB0200, so that's February of 1987. Pristine condition.
It's for sale if anyone is interested.
+1 Mine is also UB0200. It looks even more pristine, if that's possible, than yours.
Looking at the picture perhaps "pristine" isn't the right word for my lens. Considering the thing is 26 years old and was not stored as a museum piece, it's in pretty amazing condition. There are a couple minor scuff marks and there is evidence on the contacts that it has actually been mounted on a camera. It's still in better shape than my 2-year old 24-105. I doubt there are many Mk2 plastic fantastic versions still surviving after 20+ years.
It says something about relative build quality when people rather buy a 23+ years old occasion at a premium over a newly manufactured, all plastic model. I payed 1.3x what the MkII costs and have never regretted it
5D3, 5D2, Sony α6000, S90 | SY14 f/2.8, Ʃ20 f/1.8, 24 f/2.8, 35 f/2, Ʃ35 f/1.4A, 50 f/1.8 I, Ʃ50 f/1.4 EX, 100L Macro, 17-40L, 24-105L, 70-200 f/2.8L IS II, 1.4x II, 70-300L, 100-400L | E-mount: SY12 f/2, Ʃ19 & 30 f/2.8 EX DN, 16-70 ZA OSS, 55-210 OSS, Metabones SB | FT-QL, AE-1P | FD(n) & FL lenses