most, Eureka uprights....
are dated under the base, there's a circle, with a little nub in the center (we call this a nipple, for obvious reasons). this should contain two (2) numbers that make up the last two numbers of the year (minus the 19**). For instance, mine read 73. Witch then means mine is from 1973. Now there are some odd ball cases where some were not dated, the reason for this is a mystery, but just remember, the two numbers should make sense. Of coarse that not going to be from 1955 (55 in the circle), or 1988 (88 in the circle). since you know what mine says that should give you a idea...=)