Toddler communication

It's so difficult to know just how much your toddler understands when their verbal communication skills are limited. Christopher still (at 23 months) has very few words. Mama, dada, star, gah (meaning yes, here, again, come with me) being the main ones.  And a sort of moan with head shake for "no".  He can understand a lot, as evidenced by his ability to follow instructions like "if you go and get the step from the bathroom and bring it here, you can climb up onto the bed".  It's when you get to situations where he needs to do something he doesn't like that it gets harder.  How much slack do you cut him?  Robert and I made some scones while he was asleep today. While I was cooking the boys dinner, Christopher saw them on the cooling racks, and wanted one.  So I told him he could have one if he ate all his pasta. Robert ate all his pasta, Christopher was refusing to eat his. I repeated that he could have a cake if he ate his pasta first, and he started eating it. Meanwhile Robert finished his pasta so I got him a scone. I was surprised that Christopher didn't throw a tantrum over Robert eating the scone, but pleasantly so.  But if he had, would I have felt bad about not giving him one?  I can't wait for his verbal communication to catch up with his understanding.  It feels long overdue, and it's getting frustrating for both of us!