Basically your instance will start logging the numbers from the first person on your instance interacts with community AND will only log local subscriptions and votes. Obviously a bigger instance is likely to have someone connect before you more than a smaller one. It's funny because I will create a post from my instance and think it flopped, only to check it from another instance and it did numbers.

The only accurate number is the host instance. You're not thinking in fediverse terms. What about votes from federated instances? If you have some blocked that they don't the numbers won't match. What about banned users? If someone is banned from theirs but not yours the numbers won't match.