That’s possible. Systems like this have a curve. When the curve’s peak is reached is a function of how many total events act in the system. In this case, that would be the total number of people interested in voting for Black Mesa ever.
So, if the total number of people interested in voting for Black Mesa on Greenlight is (roughly) twice the number of votes required for Greenlight, then the rate will continue to accelerate to the end of the voting. If the total number is less than twice the requirement, then you’ll see a decrease in rate before the voting ends.
Also, the curve won’t be perfectly smooth, it will be a bit like a saw or zig-zaggy, with small rate fluctuations, but the curve’s mean moves in the same general direction. So, if you’re tracking the votes, don’t freak out if the rate is slightly less than it was an hour ago.