I have asked the exact same question somewhere around here a few weeks ago. Got no reply back. I think (but don't know for sure) the letters you are referring to do not make a difference, its the last part (after the first _) which identifies the radio.
My phone: Desire Z (Vision) | Rooted | PVT ENG HBOOT | S-OFF | Latest CM7 Nightly | Radio 12.28b.60.140eU_26.03.02.26_M | Modded Darkedge Red Theme | Noreve case | Screen protector
Daughters phone: Desire Z (Vision) | Rooted | PVT ENG HBOOT | S-OFF | Not the latest CM7 Nightly | Radio 12.28b.60.140eU_26.03.02.26_M | No specific theme | Breaded sock as case | Screen protector