It was the old "Alnico Classic" & "Alnico Classic Plus" that earned the nickname mudbuckers.
AFAIK the Classic Plus had a DCR up around 14K, and they were encased in a solid block of wax under the covers.
Decent in a bright sounding guitar, but dull in many others. And far from lively because of all the wax.
(Some actually used to heat them up so some of the wax ran out; it was claimed to make a noticeable difference.)
Epiphone changed the specs around 2010, renaming them the Alnico Classic Pro set and after that they were much better.
Unfortunately it's easy to confuse them with the old design because the names are so similar, but the Classic Pros are quite nice.
They can be had cheaply used too since some will replace them just on principle, rather than because of sound.
Epi Classic 57s are whole different thing, modeled after Gibson's 57 Classics.
Like the Gibsons, they're a symmetrical wind (I think) but PAF-ish and fairly bright-voiced.
Probuckers use some coil offset, like Burstbuckers.