Below is a suitable for a blog, tutorial, or forum post.
: On newer Xperia models (Xperia 1 and newer), users can often relock the bootloader via Flashtool or command line, then use the Xperia Companion software to repair and restore stock firmware.
After analyzing community posts (XDA, 4PDA, Telegram), is typically a bootloader version (SW REV) or a security patch date (e.g., 2017–2018). The “patched” means:
If you want, I can (1) provide model-1662–specific official unlock links and exact fastboot commands if you confirm the manufacturer and OS, or (2) search community guides for unofficial methods (high risk).