I've been designing injection molded plastic parts for various products for 30+ years. I'm not a materials scientist, but from what I've seen with plastics, the

I've been designing injection molded plastic parts for various products for 30+ years. I'm not a materials scientist, but from what I've seen with plastics, there will be experts who will be able to date plastic archeology to a high degree of accuracy. The basic materials of things like polycarbonate or ABS may be fairly consistent, but the additives (plasticizers, lubricants, colorants, etc) seem to have a lot more change, specialization, and innovation over time. There's a constant push-pull of wanting the cheapest possible generic materials vs wanting performance, while the plastic companies need ways to differentiate their products to make it so that very specific grades get designed in. With the right technology (e.g. chromatography or mass spectrometry) the right industrial historians/chemists will be able to fingerprint plastic objects and date them.