Its either extra content thats not part of the official release(?) or you're recalling a familar manga but forgot or your brain automatically filled in some blanks while recalling and misjudged Tharju's size?? Really not sure but I dont ever remember baby Tharju gradually growing bigger. It was straight to a time skip between Tharju's first appearance and the fake loss of the King, old reader here as well

Are there missing pages or?? I think I’ve read pages some time ago that when the baby tiger accompanies the queen to sleep at nights, there are panels showing the tiger is growing bigger and bigger…showing a period of time passed since the young king’s last visit after the queen’s heat. Am I imagining things???