There is one exception I can think of.
Let’s say we have two topics: A and B, each with 100 votes, but 20 of the users who voted for A also voted B. If the two topics are merged, it is not guaranteed that the final topic will have 200 votes because there might be some users who voted on both of the topics and the votes will not be duplicated.
The final count will be = users count who voted A + users count who voted B - users count who voted both A and B. In the example above (100 + 100 - 20 = 180).