Whether the same public key can be created by two private keys is another issue. I assume that the answer is yes, but I'm not sure. Two 256-bit numbers, which are X and Y coordinates on an elliptic curve, consist of the public key in uncompressed form. The compressed form, however, is just the X coordinate plus a bit, which you can measure the entire public key from.This implies that (at most) the room is 2^257. Because of the mathematical properties of the cryptography used, unless there is a one-to-one mapping, each compressed public key corresponds to approximately 0.5 private keys (with the same distribution you will get from choosing a random number from 1 to 2^257, 2^256 times), so some private keys can collide, while others won't.