ECP have a fitment details tab/section which will usually tell you some additional information. For example mine needed a DMF last week, two options with different diameters.
Similarly a replacement rear light cluster, had two options of either standard filament lamps or LED.
Some things are obvious but others you may need to measure or remove the part to be replaced. It’s the joy of manufacturers tweaking things each manufacturing year.
I had a kit car with a hodge podge A Series engine. Was always fun getting engine parts for that as there was no way to identify which particular version of some parts was required, unless you measured it.
If you want to pay full whack then the dealers part dept. may be able to get it right more of the time, if you give them the VIN or engine number.