Sanyo G2311 stereo fm radio

[JCB]

Why was it that Sanyo went backwards on their model numbers when the G2615 without stereo fm unless you are using the optional extra Stereocast addition but the G2311 has fm stereo built into it? 
Does anybody know the release dates for these two models?

[JCB]

Might be of interest to someone, I have just discovered that British firm Alba got Sanyo to make a Stereocast Fm decoder and badge it Alba SA1 with ‘made in Japan’ on the back of it.
It was an exact copy of the Sanyo Stereocast RB9080