A recent thread over on Typophile prompts me to explain why one sometimes sees OpenType CFF fonts that don’t actually support Greek, claiming that they do (by means of the Unicode Range and Codepage bit settings).
Originally, when Adobe converted the Adobe Type Library to OpenType, in the early stages we were thinking we wanted to be as compatible as possible with the Type 1 versions of the fonts.
In the absence of codepage bits and the like in Type 1 fonts, Windows GDI used to do a test for specific codepoints in the font to determine whether given codepages were supported, I believe one codepoint per codepage. I believe the codepoint to determine Greek support was the one for the “mu”… but it was definitely a test for a character that was present in the basic ISO-Adobe character set (now Adobe Latin 1). This even though the character set didn’t really support Greek, it just had a few Greek characters because of their use as math symbols.
So, the Type 1 fonts were (arguably erroneously) detected as supporting Greek by GDI. The idea at the time was that the OpenType fonts with the equivalent character set should behave the exact same way, and therefore the determination of whether to give them the flag saying they support the Greek codepage should be based on the same test… so basically all the fonts would claim to support Greek, even though they really didn’t.
Somehow, even though the idea of near-perfect compatibility between the OpenType fonts and their Type 1 predecessors was abandoned, this principle stuck during the initial conversion of the Adobe Type Library (“Alchemy”). Unicode ranges were set more-or-less in compatibility. Additionally, the AFDKO “makeOTF” tool used to build fonts would automatically do this, unless specifically over-ridden. So you could see third-party fonts doing this as well if they were made with older versions of Adobe tools.
I thought this was a mistake, and eventually convinced other folks of my opinion, so this decision was changed in the revision of the Adobe Type Library (“Facelift”) a couple of years ago, released about October 2007. The AFDKO was changes as well, to match this new preferred behavior.
So, you’ll find that the 1.x version of Adobe Caslon Pro built in 2001 has bits set to claim it supports the Windows Greek codepage and the Greek Unicode range, but this claim was dropped in the 2.0 version of 2007.