The next big step in the radiocarbon dating method would be Accelerated Mass Spectrometry which was developed in the late 1980s and published its first results in 1994 (3).
This was a giant leap forward in that it offered far more accurate dates for a far smaller sample (9); this made destruction of samples a far less delicate issue to researchers, especially on artefacts such as The Shroud of Turin for which accurate dates were now possible without damaging a significant part of the artefact.
Though their initial calculations were slightly incorrect thanks to the contaminants of extensive nuclear testing of the age, scientists soon discovered the error and developed methods that were more accurate, including a date of calibration to 1950.
When the half-life was corrected in 1950, the year was taken as a base date from which to calculate all resulting dates.
Therefore, any expression of “before present” will mean “before 1950”.
date of organic material - but an approximate age, usually within a range of a few years either way.
The other method is “Relative Dating” which gives an order of events without giving an exact age (1): typically artefact typology or the study of the sequence of the evolution of fossils.