The way in which you have worded your question has lead to why no one has responded.
On one hand you have a 50/50 chance of pulling out any number however; that is not the probability. It is 0.25% each pull. The first chance probability of pulling a number is 0.25% which is low. This reveals your question is not constructed very well.
It is not more likely that you will pull a number after each consecutive pull. If that were the case then each pull after the first adds 0.25%. So the second pull would be 0.5% probability.
This is not realistic but it is in line with your question.
What are the odds that a number has been stolen is more percise. After each pull there is a 0.25% chance a number was stolen.
It isnt 100% probability if you pull all 400 numbers with none stolen. This is incorrect use of the wording.