Basic Explanation:
Portals created:
Over-world A, B, and C
Nether 1, 2, and 3
If you take Over-world portals A, B and C you appear in Nether portal 1
if you take Nether portals 1, 2, or 3 you appear back at Over-world Portal A
This has been tested in realms and in a normal survival in multiple locations and different times of day. you always end up at the original portals made.
Related issues
Comments

Thank you for your report!
We're tracking this issue as MCPE-39609, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Mojang Support – ✍️ Feedback and Suggestions – 📖 Game Wiki