Eames Chair with Zenith stamp?  

Bought these two shells at a flea market. Of course the previous owner painted them white. As I was looking them over I noticed that they lacked a Herman Miller embossed logo, but they were undoubtedly Eames chairs so I purchased them anyway. When I got them home and started getting paint off I noticed a black stamp that says "Zenith" and then another word that I can't make out, but it starts "PRI....". The question is has anyone ever seen this stamp before? It appears there was a sticker prior, but had been torn off. There is also a numeric code. Is this an early model? I think they are ochre light in color, but I don't know that either. Thanks for any insights!!