Click on a circle in the chart to view Sham immigration records. You can find out when most of the Sham families immigrated to the United States. You can focus your search to immigration records dating from that era. Immigration records can tell you an ancestor's name, ship name, port of departure, port of arrival and destination.
Probably, however...: As my colleague dr. Pappas mentions, marijuana is almost always tested in urine rather than blood, so someone would almost certainly pass a blood test but is more likely to face a urine test.
Blood tests are more sophisticated than we think. While THC can be detectable in the blood of non-regular marijuana smokers up to 27 hours after consuming, regular smokers can be caught within up to nearly 90 days. Furthermore, it is not for sure: in some cases, the detection period turns out to be even longer.