Thought I'd graph time vs serial numbers to see what production volumes looked like for the years that we have data so far. Looks pretty linear to me! I only entered data where BOTH the month and the year were available, and either the engine serial number or the frame serial number were available (I entered a 0 if one or the other wasn't given).
Note the three outliers on the following graph (around 1977 and 1978). Those are for the FJ55's.