OSIRIC does not use the SRD. It just uses the OGL.
They may have produced an "OSIRIC SRD", I have no idea. but even if they have, it is a completely different animal.
1E was never released by the authors/owners. The D20 rule set was.
I think you maybe simply don't understand the distinction.
I think you might be conflating the SRD with the d20 license. There's no reason to use the OGL except for the purpose of using someone's open game content (which wouldn't necessarily be the SRD, but it usually is).
Once you've got the OGL in place, you can use IP from the SRD.
OSRIC uses a second premise, which is that one can't copyright game rules (not to be confused with the presentation of those rules, which IS copyrightable).
For example, OSRIC could have ignored the whole structure of the OGL-SRD and relied solely on the "can't copyright rules" rule, but in that case it would be missing lots of IP - the stirge is a good example. You couldn't use that monster name (it's unique under copyright law) much less couple the name with a physical description of a mosquito-bat-thing. However, by using the SRD (activated by the OGL), that name and description become usable under license.
There are clearly some gaps between non-copyrightable game rules and the SRD; anything copyrightable that didn't make it into the SRD is a blacked-out area that didn't appear in OSRIC.
On the other hand, the actual d20 license (a third factor in the OGL-SRD-d20-D&D compatibility rules), if used, would preclude the use of certain rules-changes outside the SRD. That's why OSRIC doesn't use the d20 license. It couldn't.
But you don't need to use the d20 license to access the SRD - just the OGL. OSRIC doesn't just look back to the 1e rules, it also draws considerably on the SRD for intellectual property like the stirge name and description.
I seriously doubt that Clark was saying that OSRIC had a problem as a matter of law (that would essentially be saying that the general statute had no meaning) - I think he was saying one or both of two things (a) he thought OSRIC had tripped over one of the specific tests of copyright law, either using a rule that wasn't a rule, or violating SAP, and/or (b) that WotC as a practical matter could sue regardless of merit, which could rebound on a publisher who was using it.
He didn't specify anything more than the "wouldn't touch it with a 10' pole" comment, but I really doubt he was talking about pure law in the sense of saying that theoretically it couldn't be done.