And now it's official, ATI did some selective rebranding of their Radeon HD 3000 generation to HD 4000 but this time they did it in their official Catalyst 9.1 driver.
The file called CH_75108.inf says it all. It shows 11 new cards branded as Radeon HD 4230, HD 4250, HD 4570, HD 4580, HD 4730 and finally HD 4750.
Take a quick look at this part of inf file
"ATI Radeon HD 4230" = ati2mtag_RV610, PCI\VEN_1002& DEV_95C5
"ATI Radeon HD 4230 " = ati2mtag_RV610, PCI\VEN_1002& DEV_95C5
"ATI Radeon HD 4250" = ati2mtag_RV610, PCI\VEN_1002& DEV_95C5
"ATI Radeon HD 4250 " = ati2mtag_RV610, PCI\VEN_1002& DEV_95C5
"ATI Radeon HD 4250 " = ati2mtag_RV610, PCI\VEN_1002& DEV_95C0
"ATI Radeon HD 4570 " = ati2mtag_RV630, PCI\VEN_1002& DEV_9598
"ATI Radeon HD 4580" = ati2mtag_RV630, PCI\VEN_1002& DEV_9598
"ATI Radeon HD 4730 " = ati2mtag_RV630, PCI\VEN_1002& DEV_9505
"ATI Radeon HD 4730 " = ati2mtag_RV630, PCI\VEN_1002& DEV_9505
"ATI Radeon HD 4750" = ati2mtag_RV630, PCI\VEN_1002& DEV_9505
"ATI Radeon HD 4750 " = ati2mtag_RV630, PCI\VEN_1002& DEV_9505
...