The "version date" is only really useful for the automatic version checking in AFNI (done once per week when the AFNI GUI starts, or when the user manually runs the afni_vcheck program). When the version date on the web site doesn't match the compiled-in version date, then a warning is flashed to the user as AFNI starts. I update the version date about every 6 months, so to remind people to update their AFNI binaries every so often.

The compile date is the latest and (presumably) greatest edition, and as such should be the actual criterion for updating. However, I don't want to hit people with dire sounding warning message about "out of date" versions so often, since some users tend to panic when they see any kind of warning or error message. So I settled on 6 months as a reasonable intermediate point for prompting people to update -- by then, usually a number of significant changes have accumulated.

But the nearly-weekly binary updates can be important, especially when bug fixes are implemented and the bugs are something that affects YOU (or your users). We don't have a fixed release schedule, and when a new feature is added or a bug is fixed, new binaries are built.