Unlike some states, Oregon issues two license plates per car: one for front, one for back. When you get the plates, you are given four stickers: two month stickers, two year stickers. From then on, at renewal time, all you get are the two new year stickers.
Procedurally, you are supposed to put one month sticker on each plate, in the box labelled "MONTH", and one year sticker on each plate, in the box labelled "YEAR". This seems like an easy procedure to follow. And yet, every parking lot has at least one car that has two year stickers on the back plate, and two month stickers on the front plate. More common yet is the Einstein who gets his renewal stickers and plops them over the month stickers.
I place part of the blame on the Department of Motor Vehicles itself. The year stickers have a two-digit year, and a lengthy serial number. The month stickers are also numeric, with one- or two-digits as required. At the end of the 20th Century, it was easy to see that 98 was a year, and 12 was a month. Today, it takes a bit more reckoning ability to notice that "5" is a month and "05" is a year, although the serial number on the year sticker should be a big clue.
In fact, I sent a letter to the DMV suggesting that they might want to seriously consider either (a) switching to letter abbreviations for the month, or (b) switching to 4-digit years, because the problem is going to get worse late next year, when people starting getting month "10" and year "10".