How can I check if my registration of ERC 20 EOS tokens was successful?
The easiest way to check if your EOS tokens are registered is to input your public Ethereum wallet address where your EOS tokens reside here https://eoscountdown.com/ and click 'Verify my EOS!'. This will tell you if the tokens are registered, how many tokens the wallet owns, and what it's current market value may be.
If you buy more EOS on an exchange, simply transfer them to the Ethereum wallet that is already mapped to an EOS wallet for which you own the private key. The EOS wallet will only be usable after the launch of the EOS mainnet.
Instructions on mapping your Ethereum wallet with your EOS wallet can be found here https://eos.io/instructions under 'Participating Instructions'.
You can use https://eosauthority.com/ to verify If your tokens are properly registered.