I have an SC-55 (one with just the GS logo) that has a serial starting with CD, came with 1.20 firmware. I'm assuming the ones that start with DD have 1.21. The ROM chip inside was socketed for me.
To tell which version you have: while unit is in standby (plugged in, powered off), press both instrument buttons and both midi ch buttons and the LCD should come on and tell you the version for a few seconds. I had to do it a few times to get it to show because it's not too easy to press 4 at once.
I had a bunch of winbond W29C020C spares I use when working with motherboards., they work for all my socket 7, slot 1 & socket 370 mobos, so I got a bunch a while back. I looked at the Roland chip's pinout vs the Winbonds I had, and the only difference seemed to do with writing, which made sense considering the Roland ROM is not an EEPROM.
So I YOLO'd an attempt - flashed the 1.21 firmware on one of my W29C020C, put it in, and it works completely fine, now with 1.21 😀
The interesting bit with these chips is that if you have a motherboard that takes them, you could boot into dos, remove the chip while the PC is on, put a new one, program it with the Roland rom using something like uniflash and put the original bios chip back in your PC, and the newly programmed chip into your SoundCanvas. I have an XGecu T48 programmer so I used that instead though, but I have hotflashed using a PC in the past. Just absolutely make sure you put the chips the right way or they will short/magic smoke.