I suspect that the regular JIT we tend to learn about from the Lawyers is for the practitioner and applicant community; this seems to be a "pushed" list that USCIS can control the distribution of. The website ("modern") list is perhaps "polled" by the legislative community (senators and congresspeople); and perhaps that's why only those dates are listed in this version of JIT which will not reflect poorly on the bureau. This is just a hunch; I've no basis to support my hunch, other than my general knowledge about bureaucracy.