Although it's true that only "non standard base-14 fonts" should be left un-embedded when exporting into PDF, there are reasons why other fonts are not embedded.
A bug in Canvas that causes embedding to fail:
We have found (and fixed) several bugs related to font embedding since the first version of PDF export in Canvas that supported embedding. Every now and then we receive a report of a font Canvas has trouble embedding due to an overlooked font feature.
Some irregularity in a font's data (both PS or TT fonts):
Not all fonts are created equal; some are of excellent quality, some are not, and some are just terrible. There is a lot of things that could go wrong, such as obsolete data features, wrong data versions, missing data or missing essential tables.
Font version that is not supported in Canvas yet:
The current version of Canvas does not support ALL types of fonts. For example, multiple-master fonts are not supported, synthetic fonts are not supported, and - most importantly - OpenType fonts with PS outlines (a.k.a. *.otf fonts) are not supported. Canvas support of these fonts is a work in progress. Ideally - the plan is that Canvas should embed subsets of all fonts (except the base-14 fonts). If a font does not get embedded, it is due to one of the reasons stated above.
ACD Systems of America recommends upgrading to the latest version of Canvas for enhanced performance and stability.