Basically, all the Regals with the "T" packages were "T"s (in 1986 it was a separate option group and only available with the turbo motor ... these cars were "T-Types").
In 1987, the "T" package was separated from the turbo motor (you could get an Olds 307 and still get the T package with it's trim, suspension, etc.).
So, therein lies a bunch of the confusion ... T-Type was separate and distinct to the turbo cars up until 1987. In 1987 you could order your Regal with or without the turbo motor, with or without the T package, etc. leading to some really unique (or depending on your point of view ... oddball!) combinations of options.
For example: The Leather equipped Limited with the Landau top and opera lights, turbo motor, etc. that Red Armstrong has (actually Jane's car). Or my buddy Chuck's base Regal with bench seat, column shift, little chrome mirrors and AM radio (with the turbo motor) which sat next to his other car (now his son's) with the "T" package, bucket seats and all the options (both gray!)
Originally the Turbo T was the way the the WE4 option package was described in the dealer literature and stuff. This sort of morphed into referring to any 87 Regal with the turbo motor because of all the confusion. As a result, there's all sorts of nomenclature running around and it's probably not technically correct.
Around here we like to refer to them generically as "Turbo Regals" or "TRs" to catch all the odd ball variants. Turbo Ts is usually something associated with the WE4s but often used to denote any TR with the T package (probably incorrectly).
Clear as mud?