The series 1934 FRN's from the transition period can be a hair pulling experience attributing if they are light or dark seals.
First: The terms light and dark are very misleading, let me explain. The very first 1934 FRN's had a vivid yellow green seal and numbers. as everyone is well aware of. By about mid to late 1936, the seals took on a milky / hazy cast to them, but were still yellow green.
By September of 1937, the transition began to take place, but notes printed from September to sometime in November of 1937 still were yellow green, just a darker shade.
Sometime in November 1937 to the later third of 1939, seals and serial numbers were what is now classified as VIVID BLUE GREEN seals. The earliest examples were lighter than the last yellow green (light green) seal notes, but had taken on an unmistakable blue green hue.
At last, the last color was the dull BGS notes. These have a flat / lifeless appearance to the seals and serials, but took on various hues over the last 12 years of the series.
1934 $5 FRN's should be easy to classify, as ptoduction of $5 FRN's ceased in 1936 for most districts, except Atlanta, Dallas, and San Francisco, which ceased in 1937. By the time production resumed in 1942 (1941 for Boston, New York, and Cleveland), the seals were dull blue green.
Here is a list of the last serial numbers for 1937 for the $10 FRN's 1934:
I07776000A (possibly all yellow green)
The batches of series 1934 FRNs were small at this time, so the breaks in the seal color change are anywhere from about 750,000 to 2,500,000 numbers below the highs of 1937.
Early full vivid yellow green seal printed in mid to late 1935.
Later transitional yellow green seal. These often get mis-attributed as dark green seals, but the seal still encompasses yellow green. This note is from a batch of stars numbered September 02, 1937 (D00168001* to D00180000*)
Early vivid blue green seal. Notice this note is actually a bit LIGHTER than the star above ? This note however encompasses blue green. This note was numbered roughly ten weeks after the seal color change, sometime around late January 1938.
More to come soon.