How to upgrade from really old version

(related to this topic…Upgrading from March 2016 Build)

I’ve put off upgrading for about 1.5 years (May 2016).

I attempted an upgrade to the latest version, but storage upgrade failed. The reason was that it was trying to access a Db that didn’t even exist (phabricator_packages). My guess is that I have to do some intermediate upgrades first.

If my guess is right, the main question is: how long can I go w/o upgrading? Not that I want to do it that way, but since the upgrade process is not cumulative, I would be good to know so I can schedule around it. Of course, I realize that it may not be possible to know what the mimimum is. I do know Phab docs recommend every two weeks, but that’s quite burdensome. Others use a script, but I’ve read that eventually the process changes/breaks.

Advice?

Thanks in advance.