Go the the Fix Central site and check the packaging details pages of every TL from TL 7 to TL 9 to find out what was changed. Example for TL9: IBM Support: Fix Central
No need to follow the SP links as these are updates to the TL's files usually.
Hm, yes and no. The list is huge. But most TL filesets are about a new function/feature while the SPs are fixes. The meaning of "Add" in English should be clear but even descriptions like "NPIV PHASE 1" indicate a complete new feature that entered AIX with TL9.
For a complete release there are the AIX Differences Guides but I am not aware of that such a list exists for TLs.
IZ13484 ADD MOUNT OPTION TO NOT UPDATE ACCESS TIMES FOR JFS2
IZ15252 TOPAS TAPE METRIC SUPPORT
IZ16336 HOST ETHERNET ADAPTER PERFORMANCE ENHANCEMENTS
IZ18032 TOPAS ENHANCEMENTS WITH NMON FUNCTION
IZ18796 TOPAS AND TOPASOUT VSCI SUPPORT
IZ11387 ADDING SUPPORT FOR TAPE AS VTD