I purchased a tip mission from the base while having 3 tip missions already in stock from random mobs. I didn't see the option to interact with the one I bought even after deleting the other three and being in the correct zone. Honestly I didn't think it'd let me buy a 4th but it locked out of getting the tip properly since it said I already had the contact. I was able to force it to drop the tip by swapping alignments but it shouldn't let you buy more tips than you can carry.
Edit: I still cannot access the tip, but it is no longer in my contacts.