Thanks! So to paraphrase, the ][ could be upgraded to a ][+?
Could an upgraded ][ and ][+ be upgraded to a //e? If so, how much further could you take an original Apple ][?
The //e could be upgraded to a //e enhanced. Could both be upgraded to a IIe Platinum (without the extended keyboard of course)?
The //e, enhanced and platinum could all be upgraded to a IIGS?
Could //e cards be used in an upgraded ][ or ][+ or were they totally incompatible?
Were IIGS cards compatible with the //e?
You'd think all of this would be in the incredibly detailed wikipedia Apple II pages, or Apple2.org, but if it is, it's not easy to find ...