I have just been looking at the original, yeah.
If we look at the Compilation, it's perfectly clear that if the Turks left, Shinra would never be able to find them. Shinra never found Lazard, Veldt, the other dozen Turks that already left, they only managed to get a hold of Hollander because the man was actively making war of Shinra, when he wasn't actively doing anything, he was fine for years on end. The resources that took Wutai, Hollander, Genesis and the original AVALANCHE down are no longer available to the Shinra of FFVII. If someone quit that they didn't want to, the best hope of tracking them down is the Turks, like they did, when Hojo quit, if the Turks themselves left, Shinra would be pretty screwed. The Turks would get plenty of help going into hiding from all their other Turks friends already in hiding.
Taking the original by itself, one could claim that if Shinra did manage to track their investigative department down, without an investigative department to do this for them, they'd have to submit to the superior force of SOLDIERs still under Shinras command. In the Compilation that's just not a plausible explanation. Unless Reno knows about Deepground and Weiss and Nero's appearance at the end of CC demonstrated a willingness from Shinra Inc. to start actually using them.