It is important to understand that 500 Startups consists of two separate entities/programs: an accelerator and a seed fund. It is very common for 500 Startups (the seed fund) to invest in YC startups.
To look at the flip side, it is rare for YC to invest in companies that did not actually go through YC (it has happened before, however).
To look at the flip side, it is rare for YC to invest in companies that did not actually go through YC (it has happened before, however).