It doesn't sound like anything serious going on. If you'd screwed up and overdosed them with nutes then you would see damage all over the plant. Same with deficiencies. They are going to affect a lot more leaves than just a couple.
A lot of times with leaves right at the soil you'll see damage similar to that as they stay moist all the time and often get a little mold or fungus growing on them that really doesn't hurt anything or affect the plant unless conditions like high heat and humidity help something like that to flourish.
You don't give them some bloom nutes or bloom boosters at the beginning of flowering? I dose them about a week before I flip just to "prime the pump" but do tend to feed more than I should with some strains.
I don't think you have anything to worry about unless it starts happening to a lot more leaves.
Good luck and good growing!