I thought I'd let it drop as the info is rather easy to obtain, but here goes.
Issue 1 - first batch of RPC 600's. Number on rear of board is 0197.000. 16 bit sound, can only drive a single floppy with ID set to 0. May have some pins missing on sound connector if you're fitting a 16 bit sound card. Have 'fat' SIMM sockets which can be difficult if fitting double sided SIMMs with chips close to the back edge (particularly newer 32 Mb).
Issue 2 - second batch of RPC 600. Similar to issue 1, ID number 0197.100. Still only 16 bit sound but invariably have all pins on sound connector. Normally have slimmer SIMM sockets. Missing connections on floppy drive circuitry restored so floppy can be ID 0 or 1.
Issue 3 - Final board. Introduced with RPC 700 and also the 'cut down' RPC 600 which appeared at the same time. ID number 1208.000. 16 bit sound on board. Reduced video bandwidth to meet stiffer CE standards. Improved stability and (normally) no need to remove C32 when fitting bigger SIMMs as with earlier board.