The promissory note for the Jol-Nar in twilight-imperium (4th ed) reads as:
After the Jol-Nar player researches a technology that is not a faction technology:
Gain that technology.
Then, return this card to the Jol-Nar player.
Many races have faction technologies that happen to be unit upgrades, e.g. Sol's carriers/infantry, Saar's space docks etc.
Let's say that one of these factions has Jol-Nar's promissory note. The Jol-Nar research a unit upgrade. Can the holder of the promissory note gain their faction version of that upgrade?
Note, the game that inspired this had Muaat swap their promissory note with Jol-Nar's. The Muaat note says:
Action: Remove 1 token from the Muaat player's fleet pool and return it to his reinforcements. Then, gain your war sun unit upgrade technology card. Then, return this card to the Muaat player.
The idea being that Jol-Nar gains War Suns the easy way, and Muaat gains Prototype War Sun II too.