I must be looking at something different as I can't see the marriage entries have been filled in by the same person

The signature of the Henry Bryceson who married Louisa Gray in 1821 is definitely the same H Bryceson who witnessed John Bryceson's marriage to Mary Shephard in 1818. The marriage between George Bagg and Marion Bryceson doesn't take place until 1836 - quite some time after the first two.
Henry Bryceson of electric organ fame now appears to have his own Wiki entry. His actual birth date doesn't tie up with the census returns - he was born 8 Jan 1775 in Perth Scotland (IGI) and died in June 1870 in Huntingdon.
He was the son of John Bryceson and Anna Mackie (probably Ann Bryceson buried St James Pentonville 13 Jan 1827 aged 82) His siblings were John born 1767, Catherine 1768, William 1771 and Walter 1773.
I thought that Henry and William on the 1841 census were brothers but I now think William was his nephew and he was bapt 20 March 1796 at St Andrew Holborn s/o William Bryceson and Mary Whiting. There was also Ralph Wilson born 1802 and Mary Ann b.1804 It now get tricky as there is another family born to a William Bryceson and Margaret Peacock. I’m thinking this is a second marriage - Marian born 1807 in Edinburgh (who must have married George Bagg) Thomas Peacock b 1810 Scotch Church Westminster, John b. 1815 Scotch Church and Ann Bapt at St James Pentonville in 1818 - this is the church where all the early Bryceson burials took place - John Bryceson, “our” Mary’s husband in 1824 (born about 1785), Thomas Peacock in 1826 (born about 1810, Margaret in 1828 (born about 1779) and William in 1835 (born about 1771).
All I have to do is fit “our” John Bryceson in there somewhere!
Carole