Tightness of the bulb scales may not be a good indicator for all species bulbs, but it can be true for all hybrid and species asiatics, trumpets and orientals. "Tightness" as I see it, is how solid the bulb is. A bulb that is like a solid ball, with now air spaces between scales, is the epitome of "tight".
IMO, more important is Lorn's mention of bulb firmness (in its individual parts, not necessarily as a whole). This hold true for any lily bulb. Some species bulbs (and their hybrids) are naturally loose growing, but a good quality, fresh bulb will always be firm and turgid.
