There was a lot of different combinations, I think. ( like always with Commodore products
Very old Amigas with Kick 1.2 and first Kick 1.3 Amigas had the 8371 512K-Agnus.
Then, later Kick 1.3 Amigas had the 8372A 1MB-Fat Agnus.
The last A-500s already had the A-500+ board in them ( Rev. 8.1 ) and therefore even had the 8375 2MB-Super Fat Agnus. And I think some of these very late ones also had a 8373-Super-Denise for ECS instead of the OCS 8362.
ECS is a grafic mode that needs a Super-Denise. And further Super-Denise needs a 2MB Super-Fat-Agnus to operate in ECS grafic mode. So if your A-500 had ECS it must have had both the Super-Fat-Agnus & the Super-Denise !
The difference between A-500 and A-500+ is 512k Chipram more in the A-500+, and full ECS ( Super Fat Agnus & Super-Denise ), and also Kick 2.0 in the A-500+.
The A-600 is similar to the A-500+, but has a harddrive connector.
I hope I didn't tell no bullshit - please correct me if I'm wrong !