This is a close-up of the bottom right-hand corner of the issue 1 motherboard. Just below the cartridge slot, we can see the legend "ACORN COMPUTER" although this is partly obscured by a green sticker. In the left-hand corner of the photograph is "ISS.1".

Apart from the issue number, I haven't been able to find any difference between issue 1 and issue 2. Certainly the layout is the same. Perhaps resistors values were changed or tracks redrawn or thickened.