Northwoods, Dec. 31, 1918 fell on a Tuesday ( ? when did they stop issue of a patent on New Years day ???? )
as for Dec. 25th, Christmas Day, it was not declared a federal holiday until 1870
according to one article, they started using Tuesday for patent issue around 1848
so prior to that, it could have been any day that they gave the final approval. ( as I see it )
some time back, I received a 200 year calendar booklet that gives the date and day of the week from 1828 - 2028
this booklet was put out by; Fairfiels & Ellis Insurance, 99 Milk St. Boston, Mass.
handy little book, kept by my computer.