Annie
Welcome to the community of the puzzled (or should that be confused?). I'll give my take on where we are, not least because each time I review it something else pops out at me.
I interpreted the original question as "is there any possibility WT of Willoughby is the WT son of WT and Elizabeth Grainger of Nottingham St Marys". I think we've all concluded no.
The question then becomes "what happened to WT jnr of Nottingham St Mary"
Your next question - what is the evidence for birth dates of WT snr and EG's children - see reply 32. Also Maggie's last reply giving James as 32 in 1841. My own view is that the 1806 for William was introduced by someone (it's on worldconnect) who has wrongly equated WT jnr of St Marys with WT of Willioughby. But as I think you've picked up it's all a mess.
My reply also omitted John. There is John Tuckwood cordwainer aged 25 at East Leake in 1841, but in 1851 he's in Loughborough and gives his birth place as Leake. Marriage at East Leake 1836. Also in 1814 there is a John Tuckwood butcher in Nottingham St Mary. Can't at the moment find him in 1851.
That has a bearing on your next question- 1 or 2 Tuckwood families in Nottinghams St Mary. If Leake birthplace is correct, then still no argument for 2.
The potential 1834/5 burial for a WT comes from me. It follows from an examination of the 1829 marriage; the 1835 marriage of Sarah Tuckwood to William Kidson, and subsequent data on Sarah Kidson. I can't find a Sarah Tuckwood baptism, Sarah Kidson in 1851 census is born Norwich. There aren't Tuckwoods in Norfolk. Only marriage I can find to give a Sarah Tuckwood is 1829. So it all suggests that in 1835 she was a widow of WT. That implies a WT burial but we can't find it. Which WT? I find it difficult to believe it's WT jnr. He's around 20 in 1829, Sarah Kidson / Tuckwood / possibly King would be 39. This hypothesis also requires the burial age for Elizabeth to be wrong, but we can't see another Elizabeth Tuckwood. The overall theory is
Elizabeth Tuckwood (Grainger) dies 1825
WT snr marries 1829 Sarah King
WT snr dies around 1845/35
Sarah Tuckwood marries William Kidson 1835
but it really is speculation.
And it still leaves the question of where William jnr is. Wendy's found the discharge record, but that William seems to have attested aged 18 in 1835 and be born Jan 1817. Is there any reason Wm jnr would have understated his age to sign up? He appers to hav ebeen examined at Chathom Nov 1849, but I can't see him in 1851 census. There is in FreeBMD a Wm Tuckwood died at Nottingham 1850, but that is not on the NFHS CD.