IOS-XE 3.7.4 cannot upgrade to 16.3.6 via smart-install because *new force* isn’t appended. This workaround uses EEM applets in the FreeZTP J2 switch template to download install the updated image.
Recently I received an RMA replacement for a CS-MARS-20 unit that had a failing drive. Thankfully we were able to get a configuration backup at its current version (6.1.5), so once the new appliance was received I was able to use the recovery image available from Cisco’s download site to get it to 6.1.5. After that I restored the configuration and everything was back to normal, but we needed to get onto the latest version (6.1.8).