I will email Walter and see what he has to say...
I found this in the mean time:
All tires sold in Canada must have the "DOT" ((Department of Transportation), or tire identification number, moulded into the sidewall. Our tire has a DOT number of GHYT 4501. The first two characters after DOT indicate the manufacturer; the second two characters indicate the plant where the tire was manufactured.
Next you may see an optional string of three to four characters. Our example does not include this code. Most manufacturers use these to record company specific information about the tire, and, if necessary, use them as a guide when issuing product recalls. Because they are company specific, these codes are not standardized and are meaningful only to the manufacturer.
The last three or four digits give the date the tire was made. For all tires built after 1999, this will be a four-digit number with the first two digits giving the week number, and the last two giving the year. For many tires built previous to 2000, the date indicator will consist of three digits, the first two giving the week number and the last giving the last digit of the year. In our example tire, the last four digits of the DOT code are 4501, so our tire was made during the 45th week of 2001.
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