Originally Posted by kubors
This means that we have to update our TWRP for flashing Android 5.1 roms?
Just as @Rapier
said. I have no problems flashing 5.1 ROMs on my Nexus 7 with the older TWRP 220.127.116.11.
The ROMs don't have any structural changes needing an updated recovery, what "Update AOSP base to 5.1" means is that the recovery code was updated with fixes and improvements from AOSP 5.1.