More generally, when two fonts differ only by the last bit of their name, what does it mean? Is it "the same font", but by different foundries?
The foundry FontFont, uses "OT" to denote standard fonts and "Pro" for those with extended character sets - see the "buying options" page for Meta:
Other foundries also use the "Pro" label. Fontfont's "OT" label (standing for OpenType) was more significant when TrueType and Postscript fonts were also commonly available.
Regarding your second point, when the same font is available from different foundries, this usually appears at the beginning of the name, but can also appear at the end, e.g: