Synonym means they're the exact same thing. They change those constantly, for various reasons.
Sometimes it can take a few months, or even a year or more, to ID a mystery plant, especially when they're tiny and/or etiolated, or when blooms are needed. Assigning a cultivar name is obvious in some cases, never happens in others for some plants that have too many similar choices (like African violets, and Hostas.) If a plant doesn't have one on a label when purchased, just use the species whenever there's uncertainty about cultivar.
