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:
Standard FontFonts contain all the characters necessary for Western languages, such as English, French, Spanish, and German.
Pro FontFonts support the same character set as Standard fonts, but also include more Latin-based (e.g. Polish, Turkish) languages, and often Greek and/or Cyrillic.
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:
- "Adobe Garamond"
- "ITC Garamond"
- "URW Garamond"
- FontBureau's "Garamond FB"