Hoppy,
I addition to the '33-'36 Forum, I believe you are reading the information incorrectly. Engine number 2387538 is a late Feb. 1931 engine number. From the listing below you can see that the first engine in February was 2368117 and the first in March 2433064. All numbers between those two were produced in the Flint engine plant, except for 2365895 to 2367200 which were either used as replacement or shipped to plants outside the USA.
FEBRUARY 1931 # 2,368,117 except # 2,365,895 to # 2,367,200 inclusive
MARCH 1931 # 2,433,064 except # 2,430,197 to # 2,432,000 inclusive