Hi Macrojack, ya got me... I'm among the few manufacturers dumb enough to be limited by physical-world constraints.
Seriously, I'll admit that it's possible to manipulate the shape of the frequency response curve in the bass region to give the perception of louder & deeper bass than would normally be possible, or to use resonances to boost the apparent bass (a sound that decays slower will be perceived as louder than a sound that decays quickly even if both have the same peak SPL), but there will be tradeoffs that are likely to be perceived.
[As an aside, in general I believe we should base our designs on perception, not strictly on measurements, because we listen with ears instead of with microphones; but measurements can be a very reliable tool if we can reliably extrapolate perceptions from measurements.]
The real-world in-room picture does include some complications and mitigations that can explain discrepancies between the published figures of different manufacturers. When speakers are positioned so they get a fair amount of boundary reinforcement (like on the floor and near a wall but not in a corner), we can expect approximately 3 dB per octave boost below 100 Hz or so. In other words, the deeper a speaker goes the more the room helps it out. This is more complex than the boundary-reinforcement situation I described in my post above, which was streamlined a bit for the sake of brevity.
The point-of-reference numbers I gave can be reproduced by anyone using a speaker modelling program, and are based on the Thiele-Small parameters. Midband efficiency may be higher, but usually it's the efficiency in the bass region that sets system efficiency because otherwise the tonal balance is off unless boundary reinforcement is used to restore it.
Some manufacturers design for and specify placement up against the wall or in a corner, and in my opinion that is perfectly legitimate. Some manufacturers give an "in-room" spec which includes several dB of broadband reverberant field contribution, and in my opinion this is justifiable (if they disclose it) but does work against making an apples-to-apples comparision. Finally, some speakers because of their configuration have significantly different sound propagation characteristics that make it impossible to adequately measure them by the same yardstick. For example, a line-source speaker's SPL will fall off by 3 dB per doubling of distance (under anechoic conditions) rather than by 6 dB per doubling of distance, so a 1 meter measurement will under-state such a speaker's real-world efficiency at the listening position.
Macrojack, which JBL woofer do you have? I suspect that in your 5 cubic foot box it's one of those cases where the designer has traded off some theoretically available (based on box size and efficiency) extension in favor of better transient response and better in-room behavior once boundary reinforcement is factored in. If so, in my opinion this is the ideal way to design a vented-box woofer system for use in a home - namely, not shooting for deepest-loudest-possible bass, but going for a more shallow roll-off that starts higher up.
By the way, JBL's specs for their woofers are conservative. If their specs say 97dB, that's what a modelling program and a careful measurement will confirm.
