Most other RC6 protocols differ in a more fundamental way from these.

The two main factors distinguishing RC6 protocols from each other are:

1) The value of a three bit field named M.
2) The number of data bits.

In ordinary RC6, M is 0 and there are 16 data bits.

In the RC6 used by Sky and Sky+, M is 6 and there are 20 data bits.

In the RC6 used by Replay, M is 6 and there are 24 data bits.

In the RC6 used by MCE, M is 6 and there are 32 data bits and the first eight data bits are 10000000 (binary for 128 decimal).

I'm not certain of the definition of RC6-6A, but I think it includes both the Replay version of RC6 and the MCE version. All the samples of Replay I've seen have the first eight bits 00000000 or 00000001. I expect there is some rule relating the length to the first few bits when M is 6, so a truncated 32 bit signal wouldn't accidentally decode as 24 bits. But if so, the Sky signal is an exception and possible problem. A truncated Replay signal could look like a perfect Sky signal.