As others concluded, lookup does not match partial keys. It has been on my wish list for some time, but it would certainly complicate a lot of the other functions of lookup (how about when the abbreviations are not unique, would you could the match of the stem or of the abbreviation, etc).
One way to address this is how we did this before the generalized input ranges supported lookup on words. You build a cascade of lookup stages, each of them handling the keys with length N. Keys and detail are directed to the right lookup stage. When the number of lookup stages is very large, it may be attractive to use something like 'deal secondary' to route them. If you're really looking for abbreviations (rather than partial keys) then it may be simpler to just feed the valid abbreviations for each key into the lookup table. Sir Rob the Plumber
