In answer to your question 3, I believe that most case makers since 1817, (when the modern sovereign coin was introduced), would have drawn enough gold sovereigns from the bank to provide their needs for the work in hand
Graham - Priestley seems to me to leave open the possibility of direct supply and/or the supply by one watch case maker to another ...
(page 303)
'It seems throughout the 16th 17th and 18th centuries, the Government Mint was the main recipient of gold and silver to convert into coinage, but a few refiners provided gold for goldsmiths (ref 14.). A convenient source of gold for watch cases come from melted down sovereigns of 22-caret gold.'
(ref. 14) - Statute 37 George III Cap 108 19 July 1797 (Duties on Clocks and Watches Act 1797)
(but later page 304)
'the raw material, which for gold cases was normally achieved by melting down gold sovereigns'
So at this stage, I still feel that it would be wise have an open mind and considered that the possibility exists that some gold came from suppliers. If it were to be found, for example, that the accurate chemical analysis of the cases produced by various case makers in the same year, were identical or extremely similar, this would be
one possible explanation. This hypothesis begs the who were these refiners?
Priestley continues with information that I believes gives some weight to the hypothesis ...
(page 332) - Sun Insurance Records
On the 11th November, 1797, Thomas (Helsby) is shown as a watchmaker in Vauxhall Road, Liverpool, in a brick house insured for £300. On 14 February 1821, he is listed as a case maker and has a dwelling house with workshops containing a steam engine, furnaces for refinig gold and silver, and glass grinding equipment. .... The last entry is for 20 November 1823, when his son John, is shown as a watch case maker at the Vauxhall Road address also manufacturing watch glasses and refining and assaying gold and silver - all insured for £2,200.
From this it would appear that the Helsbys were indeed gold refiners, more to the point, in the 1851 and 1861 census returns, John Helsby is listed as a watch case maker and gold assayer, From these descriptions, I infer that the Helsbys, in all probability, refined and sold gold to other manufacturers. I don't think we can rule out that refining of gold, in the Liverpool area, was done by a limited number of companies.
I also believe the use of coloured gold on Liverpool cases at this time may be relevant. I have formed the impression that Liverpool made, Chester hallmarked, 'coloured' gold cases were exported to America in significant numbers, where they were admired and desired. Might this encourage the use of specialist suppliers, such as the Helsbys? I also wonder if it might present a further challenge at the time of assay. Priestley provides the analysis of coloured golds on page 309, with references numbered 21-25, unfortunately, these appear to have been missed from the list of chapter references at the end of the book.
Rather later, but of related interest, the exchange between Ralph Samuel (partner in Jacob Lewis Samuel & Co. watch case makers, Liverpool) and the 1856 Commons Select Committee to review hallmarking practices, is worthy of a read (page 333).
Chairman:
has the Act of 1854 lowering the standards of gold, enabled you to compete with the manufacturers of the United States in gold cases?
Ralph Samuel Esq:
No, the Americans come here and they offer me orders from one to 800 at a time, providing I will put 18 carat upon a 9 carat case, but I would never so do.
I make no comment on the politics, but I do wonder whether one might read 'Liverpool agents for the American market' rather than Americans.
So I reiterate that while I feel that this subject is one that can be discussed and enjoyed, at length on this forum, it would need a significant research effort to achieve a meaningful conclusion.
John