Of course--I'd seen the database downgrade fix before, but had forgotten it. I'm now happily tracking MOODLE_33_STABLE.
For the benefit of anyone coming along later who may see this, the correct SQL query is
update mdl_config_plugins set value = '2017050214' where plugin = 'mod_attendance';
where the value to use in place of '201705214' the the value of $plugin->version in version.php of /mod/attendance/version.php. (That's *so* close what you had, Dan, that it was dirt simple for me to tweak it. But a future admin might or might not have the right context for it to be so simple.)
Thank you again!
Peace,
--Peter