Sixchannel, Misha (Rustyspoon) has nicely responded to the concerns you raised. I would only add that I do not expect software to introduce new features that can be used on older versions, and I think that practice is normal. For example, I use the DAW Studio One. They just introduced version 7. Version 7 loads a project written in my prior version (6.5) just fine, but when you go to save, it will first give you a caution that if you continue with the save, the project can only be reopened in version 7 from then on. I think that's fair.

Specifically, about BIAB, this subject was raised before, maybe within the past year or two, when someone asked if the newest styles or RealTracks could be used in an older version of BIAB. Don't hold me to this, but I think the answer was sometimes yes, sometimes no. The biggest hurdle was selecting the new tracks because they were not contained in the index that had been made without knowing of their existence. I believe they could be located manually and would work, however don't hold me to that either because I did not need to test it, having purchased the upgrade.

BIAB 2025 Win Audiophile. Software: Studio One 7 Pro, Swam horns, Acoustica-7, Notion 6, Song Master Pro, Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus 192 & Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors.