When a likely or known "older" item is found in a known "newer" site it is referred to as deposition lag.An example of this is the finding of a few pontil scarred utilitarian bottles among otherwise late 19th or early 20th century refuse.As Berge (1980) noted in referring to bottles, the "..of manufacture of glass containers provides observable attributes which seem to be very useful in a classification of these artifacts." Thus, this page.
Even given these descriptions beginning often mistake a machine made Owen ring on the base of a bottle with a pontil.
(Specifics on what a pontil looks like or how to tell the age based on the mold seam can be found in Bottle Basics.) While these two characteristics are often a strong clue to age, readers will be further helped by developing an understanding how the various categories of bottles changed over time.
This technology lag makes some diagnostic characteristics better than others for dating. As a corollary to #1, consider the following quote: "Treat terminal dates with care.
We can always have some indication of a starting date for a technique if we can find who first put the idea into practice.
Additional reference materials outside of this website must often be consulted to narrow down the date of any item as far as is possible and to really get a "feel" for the history of the bottle in question.