You can see what version of defMON you have by looking in the status bar when the program starts up. The version numbers are essentially just date stamps that reflect the day when the program was compiled.
If you got a version of defMON that is not available on this page, feel very free to add it here. Especially if you have an older version than the ones available here, as many of the older versions are lost.
For reference: If SHIFT+N is pressed in the sequence list, defMON will copy the current sequence (the one that the cursor currently points at in the sequence list) to the Next empty sequence. If SHIFT+U is pressed in the sequence list, the current sequence will be copied to the next sequence that is Unused in the sequence list (no matter if this sequence is actually empty or not!).
The hardware sync interface is available from Scannerboy at the chipmusic.org forum, right here.
The first publicly available version of defMON was the one that was “cracked” by Genesis Project in 2013. You can find it on CSDb. That version differs in some ways from the “ordinary” versions used by people like Goto80, Ilkke, and others.