Only a partial answer, but if you’ve flashed, then the signed files are removed after the flash completes. However, you can tell it to leave those in place, and then see if they are there after (I don’t know about during mass flash, I only know about the single flash case). An example to generate the files, but not actually flash, and then leave the files in place:
Note in the above that you have to specify a keyfile (I can’t tell you the procedure for that part). Once this “no-flash” version is complete you can search for files with a file name extension “.signed” in the “Linux_for_Tegra/bootloader/” and “kernel/” subdirectories (or subdirectories to those directories). If you were to actually flash (leaving out the “--no-flash”, then those are basically the files which would be used.