Its just a version.
Lets look on the 370.
"%AMD6810.1%" = ati2mtag_R575, PCI\VEN_1002&DEV_6810&REV_00
"%AMD6811.1%" = ati2mtag_R575, PCI\VEN_1002&DEV_6811&SUBSYS_0B001028&REV_81
"%AMD6811.2%" = ati2mtag_R575, PCI\VEN_1002&DEV_6811&REV_00
The chip is the same R575. Ids under and over matches the 270. Note I only posted 3, there are too many to post for Pitcairn.
The info that device manager would show:
AMD6810.1 = "AMD Radeon R9 200 Series"
AMD6811.1 = "AMD Radeon R9 370"
AMD6811.2 = "AMD Radeon R9 200 Series"
Same applies for the 360 for example. Its the R505 chip, a less used chip:
"%AMD6658.1%" = ati2mtag_R505, PCI\VEN_1002&DEV_6658&SUBSYS_293C1462
"%AMD6658.2%" = ati2mtag_R505, PCI\VEN_1002&DEV_6658
"%AMD665C.1%" = ati2mtag_R505, PCI\VEN_1002&DEV_665C&SUBSYS_29321462
"%AMD665C.2%" = ati2mtag_R505, PCI\VEN_1002&DEV_665C&SUBSYS_29341462
"%AMD665C.3%" = ati2mtag_R505, PCI\VEN_1002&DEV_665C&SUBSYS_293B1462
"%AMD665C.4%" = ati2mtag_R505, PCI\VEN_1002&DEV_665C&SUBSYS_8770148C
"%AMD665C.5%" = ati2mtag_R505, PCI\VEN_1002&DEV_665C&SUBSYS_9260148C
"%AMD665C.6%" = ati2mtag_R505, PCI\VEN_1002&DEV_665C&SUBSYS_9260174B
"%AMD665C.7%" = ati2mtag_R505, PCI\VEN_1002&DEV_665C
"%AMD665D.1%" = ati2mtag_R505, PCI\VEN_1002&DEV_665D
"%AMD665F.1%" = ati2mtag_R505, PCI\VEN_1002&DEV_665F&SUBSYS_0B041028&REV_81
AMD6658.1 = "AMD Radeon R9 260"
AMD6658.2 = "AMD Radeon R7 200 Series"
AMD665C.1 = "AMD Radeon HD 8770"
AMD665C.2 = "AMD Radeon R9 260"
AMD665C.3 = "AMD Radeon R9 260"
AMD665C.4 = "AMD Radeon HD 8770"
AMD665C.5 = "AMD Radeon R9 260"
AMD665C.6 = "AMD Radeon R9 260"
AMD665C.7 = "AMD Radeon HD 7700 Series"
AMD665D.1 = "AMD Radeon R7 200 Series"
AMD665F.1 = "AMD Radeon R9 360"