I just had my Oliver No. 9 chassis apart yesterday and noticed on the underside of the main carriage rail/escapement assembly, there is a stamped code in the cast iron, nickel plated rail support. This reads: 3-L-16. The serial number of the typewriter is in the 6XXXXX and looking at the typewriter database, it suggests that the machine was made roughly in 1917. This code on the underside of the carriage rail assembly looks like a date code. My hypothesis is that 3 represents the day, L represents the month, and 16 represents the year. 
Days of the month are hard to represent using a single letter character, which is why I think the '3' represents the 3rd day.
Months of the year could be easily represented by letters and 'L' would be 12 if we're counting A - L in ascending order, meaning 'L' represents December. 
The last two numerals, 16 may easily represent a code for a year.
Using this form of date code, Oliver could have produced machines all the way to the end of the 20th century, without any confusion.
Does this theory of the date code have any merit in that, am I correct 3-L-16 represents both a production date and December 3rd, 1916? That would align with the date range seen on the typewriter database. 
Finally, if this is so, can we check all our Olivers, collate this data, and add it to Munk's work?
Thanks all,
Phil Forrest