how do i recover an inconsistent backup after another full backup without restoring the new full backup?
No.

About RMAN Incremental Backups


  A level 1 incremental backup can be either of the following types:
  
  
  A differential incremental backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0.
  A cumulative incremental backup, which backs up all blocks changed after the most recent incremental backup at level 0.
  


Your recent incremental backups contain changes since your another full backup, not the previous full backup.

But you can still recover your database using archivelogs.

Edit: and here is a demo: https://pastebin.com/kn2R5FXa