This website implies that the 20A was introduced in response to the Mavic Module E, which sounds very plausible:  http://cyclespeugeot.web.fc2.com/reminiscence/araya78.htm

Earlier decal appears to suffer terrible from sunlight. I have a couple of these where I could only make out the stripes & couldn't ID the rim, until the above image was posted to a Facebook group (permission gained to use image)

ERD for 700c is measured.