The recycling of plastic products becomes increasingly attractive not only from an environmental point of view, but also economically. For recycled (engineering) plastic products with the highest possible quality, plastic sorting technologies must provide clean and virtually mono-fractional compositions from a mixture of many different types of (shredded) plastics. In order to put this high quality sorting into practice, the labeling of virgin plastics with specific fluorescent markers at very low concentrations (ppm level or less) during their manufacturing process is proposed. The emitted fluorescence spectra represent optical fingerprints" - each being unique for a particular plastic - which we use for plastic identification and classification purposes. In this study we quantify the classification performance using our prototype measurement system and 15 different plastic types when various influence factors most relevant in practice cause disturbances of the fluorescence spectra emitted from the labeled plastics. The results of these investigations help optimize the development and incorporation of appropriate fluorescent markers as well as the classification algorithms and overall measurement system in order to achieve the lowest possible classification error rates.