Copied SSHD to SSD, what happends with Time Machine?

So, I just recently upgraded my MBP to an SSD from a Hybrid Drive (both were 500GB). I did a complete drive copy using Super Duper.

I have been performing Time Machine backups to an external USB drive for several years, it has 1.5TB of space.

I can see that Time Machine thinks it's a new disk, and wants to perform a / scan. What are the implications to writing the new disk backups to same Time Machine volume as the old one? Does it keep both until space is gone? Are they treated as two different systsems? Or is the data considered one stream?

I would expect the former, but am not sure

I'm considering just going and getting another disk anyway to be safe, but would like to know.