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I meant to say that I don't see the point of that preamble statement, which is why I misinterpreted it. In a hailstone sequence a repetition of a number is impossible, so each grid has to consist of all different entries.

Sorry, ignore my last comment. I was forgetting that the first grid isn't one sequence of numbers, but numbers from many different sequences.

I have filled in the first grid except for 7d. I have u = 9 but that would leave U = 18 or 28.
7d would then be either 21 or 31.
I must be missing something.

Ah- just seen the solution to my own problem. 28 is already a letter value!

The entries in the first grid aren't by derivation hailstone numbers at all, but the answers to expressions made up of hailstone numbers. Of course any integer greater than 1 can appear in a hailstone sequence ;-)