There is no such thing as a Pro Logic or Pro Logic II recording. Those are brand names for two of the many decoders that decode Dolby Surround encoded recordings. That's why you will never see a DVD labeled "Dolby Pro Logic". They are labelled Dolby Surround.
Matrix decoders work by analyzing the phase and amplitude relationships of the two stereo channels. When the same signal appears in both front speakers, in phase, it goes to the center channel. When the same signal appears in both front speakers, out of phase, it goes to the surround channels. When a signal appears in just one front speaker, but not the other, it stays where it started.
Obviously, this is very simplified for pure sine waves. Actual recordings are very complex so this decoding is quite dynamic. Variations in how much the signals are moved around under particular circumstances and other steering tricks account for the differences in performance. For example, wide center width on DPLII tends to move less signal to the center channel, narrow center width tends to move more to the center, etc.
Pro Logic II produces somewhere in the gray area between 4 and 5 channels. The basic decoding produces front, right, center, and a mono surround channel. However, steering logic can provide some stereo separation for two surround channels -- depending on the source material, etc. But, fundamentally, Dolby Surround recordings are 4-channels (front, center, right, surround) matrix encoded into 2-channels.
If you have a 6.1 or 7.1 channel, a second matrix decoder (Cirrus Extra Surround, Dolby EX, DTS-ES matrix) works on the two surround channels from the DPLII decoder to derive a third center surround channel in much the same way that Dolby Pro Logic derives a front center channel from the two front channels.