So the creator of the Dota Anime show mentioned that there was actual meaning behind how they came to this number on the world iteration that anime took place. I tried looking up different things and finally came to below conclusion.
So this number is something involving the number of matches played in Dota 2 game as invoker hero. I tried to validate my theory by going to
SELECT
count(*)
FROM player_matches pm,matches m
where pm.match_id = m.match_id
and m.start_time <= 1616610600
and hero_id=74
and game_mode = 2
and leaver_status=0
The above query should give you a number 13274 which is as close I could get. I only counted matches played before the Dota Book 1 release date (Mar 25-2021) as it could be the next match which invoker was playing? I don't know, but here is something for you all geeks to look into.
Source: https://www.reddit.com/r/DotA2/comments/wruzxc/i_have_a_theory_for_12403rd_world_iterations_in/