Duncan's "Trembucker" bobbins are physically longer than Duncan's standard-spaced models. In contrast, most pickup mfrs simply space the poles wider inside the traditional bobbin geometry for their F-spaced/52-53mm models.
For example, a standard-spaced DiMarzio and an F-spaced Dimarzio both use bobbins that are ~65mm long.
A "Trembucker" uses bobbins that are ~70mm long, compared to "SH" models at ~66mm long. I don't have any Gibson pickups on hand to check at the moment, but I'd hazard a guess that they simply use a wider pole spacing on standard-length bobbins, similar to what DiMarzio does.
It's that extra bobbin length of Duncan's TB models that results in an increased DCR due to the extra wire needed to cover that additional length with each wind. But also keep in mind that a "JB" in standard spacing at 16.4K and "trembucker" spacing at ~17K sound 99% identical.
On the other hand, taking a standard-spaced model and winding it up to that same "~17K" value would give you a noticeably different sound.