Another sweetcorn question

Not a bad job surely. They will taste good , have two instead of one !
If the cobs are lacking kernels it is a pollination problem and leaving them longer will not help.
If the kernels are small it may be due to the variety grown.

Size is not everything..........enjoy ! 

If the kernels that are there ooze milky fluid when you push your nail into them, then they are ready to eat, whether they are big or small

I was also unsure when to harvest as I found the same as you but have learnt that the whole silks right up to the husk must be chocolate brown. I then waited a couple of weeks and found the kernels were bigger, yellow and still milky when pierced. Sometimes kernals were missing from the top but only a few centimetres. I'm growing the variety Lark and they've done really well.  I also succession sowed and now eating this batch. Lovely.