Some of us add lots of cars as "unknown", because we do not all know all the cars (e.g. except for 90s Caprice & Crown Victoria, I usually cannot identify US cars very well, and I am unable to put years on them).
So it is not a big problem. It is better to contribute with "unknown" cars than trying to guess and having other people correcting those that were false (but if you are sure, or nearly, for a model, you can submit it as you identified it).
Also check the "Coming Soon" topic to not make captures that another admin has planned to do soon, as it would be a duplicate work.