Do you know that GTG runs a blog? Maybe not as nice as ours ;), but I found on it a very interesting article about the limits of certificates in 18xx games.
We have never had the opportunity to write about it, and the topic has been very carefully elaborated, so we would only recommend reading it on this page: https://www.grandtrunkgames.com/blog/how-many-certs-do-you-lose-to-the-game