Perhaps Neri went to return the lupara to the Props Department, where he filed it under "F"--for Fortuitous Gadgets.

Seriously, Olivant's right: it's yet another hole in the Swiss cheese screenplay of GFIII. If I bend over backward--far
backward--for FFC, then maybe he was trying to reinforce Vincent's growing indispensability to Michael by having him, not Neri, spirit Michael away from the massacre.