Again: a height-to-hash translator might be useful in general, still it's no use for SPV wallets.
If you think FCU is important to SPV client, you should consider knowing where to start and end FCU is also important. Since you already know where to end it, it does not make sense that you think knowing where to start is not important.
Oh my.. it's getting clearer that you two didn't understand a word of what I said. I'm giving up, good luck!