Although I am not familiar with the code base, my sense was that there are many of these constant sets. For instance, if I search *.php files for the regex 'define *\(' I get 2124 matches. If I then search for 'define *\(.*(true|false)' I get 334 matches. That leaves quite a few, many of which are likely to be in constant sets. I'll look a bit more closely at the DB schema for integers that look as though they might be defined in sets.
At first blush, there seems to be a need for only two tables; one to name the set, and the other for the actual names and values.