Everything from LC to LC475 all had the screw. I do remember a batch of Performa 400's that were delivered without the screw. We had to send a screw to each school who requested them.
Keep in mind this was my experience with units coming from the Singapore factory. Things could have been very different for units coming out of the Cork factory.
Remember that (unlike here in the UK) "LC" was the education series in some regions, Performas sold to home users might have been sold without screws in some regions.
I guess basically we can't know for sure in all regions / markets.
But it sounds like they fitted a screw to all the educational units and with good reason!
I love these little bits of knowledge that have been lost to time. Stuff like that is hard to know unless you were involved/familiar with it at the time.
Also the LC and LC II had the Control Panel disable jumper so schools could lock kids out of messing up the system settings. But that didn't last long as a feature and Cuda dropped it entirely (it was only possible on Egret-based machines, and not all of those).
The jumper block is between the battery and the floppy connector, at least on the original LC. The pair of pins closest to the battery should be labeled "CPE", and jumping them should disable the Control Panel.