As a result of searching, there was such a function before June 11 1999.
wiki.project1999.com/Patch_Notes
High-level non-player characters with the ability to summon characters can only use the summoning ability if the characters cause more than 10% damage to the NPC.
I couldn't find it in the patch note before this fix.
Then, did summon exist from launch date(March 16, 1999)?
But summon is kind of cheap trick to prevent easy farming of High-level(51+) mobs...
Don't you remember anyone?
http://www.project1999.com/forums/sh...ad.php?t=16165
Nilbog: All level 51+ npcs have gained the ability to summon.
In p1999, summon was added after plane of sky.