So after looking around the drop tables, it turns out that the mothership used to have an equal chance of dropping either nanoforge, and thus they could drop two pristine, two corrupted or one of each with equal chance.
With a simple fix in the salvageable objects file it can be reverted, should it be of your interest.
You'd only need to go to starsector-core, data, campaign, procgen, salvage_entity_gen_data.csv and open it with a text editor.
And below where it says derelict_mothership, replace:
rare_tech:1",derelict,1,1,45,60,,3,1,derelictMothership
with
nanoforge_always:1",derelict,1,1,45,60,,3,1,derelictMothership
It will work even in an already created seed, salvage drops are determined by the seed, but the parameters applied to those drops can be changed at any time before interacting with the objects.
Already tried it with an ongoing save file and modifications would apply every time, so if you have a save ongoing and you want those rules to apply, you can probably do it safely as long as no mod you have affects motherships' drop tables.