Ron, IMHO, you cannot go very wrong if you decide to end your iron set at approach (gap) wedge from the original set, or better said, to the shortest club that you tend to use as an iron (for full shots).
The sand and lob wedges are speciality clubs, therefore, their choice should be much more dependent on many factors, such as e.g. weather conditions in which you play most, humidity of the ground you play the most, sand structure, rough type, etc.
The parameters of SW and LW from a given set (bounce, reliefs, grinds, sole width, leading edge curvature) may usually match only small percentage of the golfing population. If you are inside this - it's nothing wrong for your game to use those wedges from the set and it does not matter if you use them or most famous wedge names. But if requirements for your wedge game are different - you have no choice but to put different SW and LW into your bag.
The most important always is to know what type of wedge suits your game. If you read Tom Wishon revert to the pages in "The Search..." book that concern wedges. If you are still not sure - post your answers for the following questions:
- are you a digger or a sweeper with wedges, i.e. your misses are rather fat or thin shots ?
- what kind of around-green roughs you play most - thick, light, short ?
- what kind of sand you play most - fluffy, packed, wet, etc. ?
- are fairways that you play most humid or dry ?
Cheers
