Anything's possible. It would've been an oversight, though, as indeed the first GM capable synth, the original SC-55, had no GM subset mode separate from GS.

Does a GM Reset alter the sound compared to GS in the later version modules? With Yamaha stuff, drums certainly do change between their two modes. Something like Duke3D will stay in whichever mode you set beforehand.

My 1.20 MKI model has Init GS/Init M32 and Init All -- what is Init All if not for GM?

infiniteclouds wrote:

My 1.20 MKI model has Init GS/Init M32 and Init All -- what is Init All if not for GM?

"Init All" is the equivalent of a factory reset. It would remove any changes you had made, not only to the various parts, but system parameters. In fact, I'm inclined to think that it is a "Factory Reset" + "GS-Init".
Not the same thing as a "GM Init" at all.

According to the manual, a GM reset will cause NRPN Bank Select messages (Non-registered Parameter Number) to be ignored. I am not aware of any other effects.
I just wonder if there are any known games that send erroneous NRPN messages.

tpowell.ca wrote:

According to the manual, a GM reset will cause NRPN Bank Select messages (Non-registered Parameter Number) to be ignored. I am not aware of any other effects.
I just wonder if there are any known games that send erroneous NRPN messages.

NRPN messages and Bank Select message are 2 separate things. Bank Select is a normal controller message. SC-55 in GS mode understand Bank Select MSB (CC# 0) messages and switches to different variation banks according to these messages. SC-55 always ignores Bank Select LSB (CC# 32) messages. On the other hand NRPN messages are used to alter some internal properties such as vibrato rate/depth/delay. So according to your referred documentation in GM mode the synth ignores Bank Select controller messages (thus variation banks) AND ignores GS specific NRPN messages.
Later Roland devices (SC-88+) are sure to behave like this in case they receive GM system ON messages, but I do not think it's also true for all kinds of SC-55:
Apparently not all GS-only sc-55s are the same, some are GM

Cloudschatze wrote:

When an SC-55 receives a GM System On message, it either: 1. Treats it exactly the same as a GS Reset (ver. 1.xx SC-55), or 2. T […]
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When an SC-55 receives a GM System On message, it either:
1. Treats it exactly the same as a GS Reset (ver. 1.xx SC-55), or
2. Treats it as a GS Reset, but also sets Rx.NRPN to "Off." (ver. 2.xx SC-55)

No SC-55 ever disables reception of the Bank Select when receiving a GM System On. That behavior was first implemented with the SC-55mkII.

Regarding games GM mode can solve some CTF related problems (no instrument can be heard) in case of SC-55mkII.