I have a Murano with an 1846 date cane. My has small, thin black letters on on oval tablet, and is much less common than the version that has a bold date in a white cane squashed between other millefiori canes. I have seen the dates 1846, 1852, 1869, 1885, 1887 - there may well be more, tailor made as Kev H suggests. 1846, 1869 and 1885 seem to turn up quite a lot.
If you find a weight with a 19th C date in it, the odds are it was not made in the 19th C. Whilst there are genuinely dated French, Bohemian and American weights from the 1845 - 1853 period, I estimate that 90% or more of the 19th C dates are either Murano (with dates as above, and others) or '1848' dated Arculus / Walsh Walsh weights.