The wording on the terms and conditions is
If you enrol in IHG® Rewards Club at the time of your initial stay in any IHG branded hotel excluding ANA partner hotel worldwide, you will be awarded 1,000 points for that qualified enrolling stay.
I'm guessing they could successfully say that standing at check-in could easily be classed as "The time of your initial stay". They would argue the minute you walk in your stay begins and so on.
I agree it sucks though - totally!! I'm not sure why they do that as with higher costing stays the new member would earn a decent wedge of points and that large early deposit may just encourage them to book their next stay with IHG and maybe change their behaviour resulting in less stays at a competitor whereas this has probably encouraged the OP to look elsewhere first in future.
Also isn't there something about extended stays not qualifying for points or am I thinking of another programme? If it is IHG would 34 nights have been too many for points?