Lower leaves turning yellow on seedlings

[Tomatovator]

I know I have read something about this recently but I can't find it now. I have a good number of plants that are about 5 weeks old, 5" to 6" tall and in 7oz. cups of potting mix. Most of them look fine. Two Costoluto Genovese and one Early Pick have the bottom 2 leaflets turning yellow. The plants actually look great and are the larger of the bunch. I used some diluted seaweed emulsion about a week ago but no help. The leaves are getting more yellow. I don't think I've been over-watering but who knows could be more dense packing of the potting mix in the affected cups so they are not drying out as fast as the others. I'm not that concerned about curing the condition for now but want to know if the plants will be OK if the bottom leaflets are cut off and they are planted deep when the time comes. I would also like to point out that it is not the cotyledons that are turning yellow. I pinched those off a while ago. It is the first set of true leaves that is turning.