Wow. Hoodathunkit that they have such sophisticated rope tracking measures. Each rope must have a unique serial number and GPS locater embedded within its course fibres...
Manufacturers have distributors.
Distributors have vendors.
Vendors have records and cameras.................
Actually, I think they are just looking to see if He had purchased identical rope in the recent past, which if true, would cast even more doubt on his story. Yet, that piece of rope could have come from a coil that had been sitting in his, or a friends, back room for years.