Language repertoires have been traditionally construed as a set of chronologically determined compartments (first language, second language, etc.), a scheme which upholds several validity and ethical issues when operationalized in research and education (Ortega, 2019). Complex dynamic systems theory (also complexity theory, here CDST) has been hailed as one solution moving forward, but its applicability to plurilingual settings requires further testing. This exploratory study contributes by examining whether inherent properties of complex dynamic systems manifest in the perceptions that plurilinguals have as their language systems change over time. Using retrodictive qualitative modelling (Dörnyei, 2014), this study discerned the developmental trajectory of changing language systems by working backwards through data collected during an observation window. Over a 3-month period, three plurilingual individuals assessed their language systems through weekly surveys and participated in open-ended interviews. A three-stage phenomenological analysis evaluated the data against CDST's theoretical prism to identify five CDST properties (attractor states, phase shifts, co-adaptation, self-organization, and emergence) in the participants' perceptions of their changing repertoires. Results indicate that plurilingual repertoires exhibit the aforementioned dynamics, although evidence for emergence was less certain. Importantly, this study shows that CDST dynamics are discernible in an individual's perception of their language development over time.