Nor can the measured Pb isotope ratios be used to somehow decide what proportions of them are the initial Pb without recourse to unprovable assumptions about the mineral or rock’s history or their interpreted U-Th-Pb ages within an assumed deep time history.
Nevertheless, the ultimate foundation of this U-Pb dating methodology is the assumption that the earth formed from the solar nebula.
Note that the serial number information below is fragmentary and incomplete, and many bikes have proven to be much newer than the serial numbers would suggest.
It appears that Raleigh recycled many of the older serial numbers in later years, so there are lots of bikes from the 60s and 70s that have serial numbers that would suggest much greater age.
In 1974, an entirely different numbering system was introduced for the higher end (531 and subsequently 753) Raleighs. It indicates the year of manufacture, the decade being assumed (i.e.
Serial numbers should begin with a "W", which stands for Worksop, the facility that produced theses frames. This alphabet indicates the fortnight in which the frame was built (i.e. "4" could be '74 or '84; it is up to the interpretor to know enough to tell if the frame is from the 70's or 80's). At this point, these appear to be some sort of sequence, but this has not been substantiated.
The company was sold to a group of money manipulators who shut it down in hope of making a quick profit by selling off the assets.
The Taiwanese company Sunrace bought the equipment, stock and rights to the name and is back in business.
a "G" serial number may have been built into a bike in 1973, but the frame may have been built in 1972).
Most older Sturmey-Archer hubs have two or three-letter model codes, which are usually stamped onto the hub shell.
Conveniently, they also usually have the month and the last two digits of the year of manufacture stamped onto the shell.
Various methods have been devised to determine this initial or common Pb, but all involve making unprovable assumptions.
Zircon does incorporate initial Pb when it crystallizes. It cannot be proven that the Pb in apparently cogenetic U- or Th-free minerals is only initial Pb, and that it is identical to the initial Pb in the mineral being dated.