One of the orthodox ideas that exists has to do with date encoding within a serial number of a Japanese frame manufacturer.
This in itself is not very important but it demonstrates that once an idea has been put out into the public realm and that idea takes hold, then it is difficult to change the public perception of that idea.
The specific serial number type is the "N" prefix serial number, followed by a digit which indicates the year of frame manufacture, followed by a letter which indicates a time period within the year, followed by four digits. This format of serial number is most often scene on several models of Centurion brand bicycles from 1978 to 1989. This format of serial number is also found with other brands including, but not limited to: Diamond Back MTBs, Novara, and Terry.
It was the orthodox opinion on bikeforums.net that the time period for the letter was a fortnight.
In October of 2017 I showed an analysis of this format of serial number and demonstrated that the time period represented by the letter was more probably a month than a fortnight.
I will not repeat the report on the analysis here. The analysis is in this post in the centurion serial number database thread:
https://www.bikeforums.net/19917187-post2203.html
To my knowledge, no one has contradicted or questioned this analysis.
However within bikeforums.net the belief persists that the letter represents not a month but a fortnight.
Another note on this topic. Bicycle manufacturing goes on a yearly cycle. Bicycle production at a factory is not constant from month to month.
Distributors and retailers in North America order seasonally. They order at the end of one year for the next years spring.
Bicycle factories do much of their production in the last quarter of the year.
If the time period letter in "N" type serial numbers is for a fortnight there should be plenty of letters T, U, V, W, X, Y, and Z. These letters would represent the fourth quarter. In the Centurion serial number record of "N" type serial numbers these letters are never reported or almost never reported. This would mean that almost no bicycles were manufactured in the fourth quarter by whoever was the manufacturer.
In the monthly proposal the Letters N, P, and S would represent the last three months of the year. These letters are reported frequently in the N serial numbers. This correlates with the frame manufacturing season.
Does the letter in the "N" type serial numbers represent fortnight or month? You decide.
- - -
"Hey, what was that that just hit me in the head. It didn't hurt a bit."
Johnny Rotten on stage at the Winterland Ballroom, San Francisco, California 01/14/78