Legal Question in Criminal Law in California

If the warrant was served correctly, then the error you describe shouldn't matter. A "technicality" is something that *doesn't* change the outcome, not something that does.

The "return" (the receipt they left) having the wrong address doesn't necessarily invalidate the entire warrant. Having said that, your friends' attorneys should be looking closely at the warrant to make sure it was valid and there isn't a motion to quash the warrant and suppress the evidence seized.