Some day ago I had problems with two mobile devices, the last one was with Nexus 7 tablet; the problems started because of so stupid issue I confused my Nexus 7 V2 (2013) with a V1 (2012) and of course flashing recovery and system images everything was broken. Finally, I had to re-flash stock images for recovery and system. In the middle of the process and thanks to XDA-Developers, I found a really useful toolkit called SkipSoft.
I just want to remark the work done by people of SkipSoft and give thanks to them for their great work. They simplified long processes downloading and flashing images to my devices to a simple wizard process with their scripts.
BTW, thanks also to Pof who gave me the inspiration for solving my mistakes flashing improper images to the Nexus 7.