OK. Utility is complicated. Rather than just worrying about the 1931 company Utility Motor Cycles Pty Ltd, there are two others that are clearly in play: Findlay and O'Connor Pty Ltd, and R A & F Findlay Pty Ltd. You can add in Pioneer Motor Cycle Exchange Pty Ltd, and "the Royal".
All are linked. Findlay and O'Connor, trading sometimes as "The Royal", sold secondhand motorcycles in the 1920s from 319 Swanston St. Pioneer Motor Cycle Exchange Pty Ltd was formed in 1926, presumably to take over the business of The Royal (Findlay and O'Connor), and traded at the same address, with Jack Taggart as manager. When Pioneer was liquidated in 1931, a new company - Utility Motor Cycles Pty Ltd - rose from the ashes at the same address. The subscribers were former Pioneer manager Jack Taggert and Ernest Louis Andrea. Here's the interesting bit: Utility bought and sold secondhand motorcycles. By 1933 there were Utility bicycles; Utility motorcycles appeared in 1934, but not obviously associated with Utility! Instead they were shown and sold, from March 1934, by Findlay and O'Connor Pty Ltd, at 299 Swanston St and 320 Elizabeth St.
Now at the end of 1933, Findlay and O'Connor were selling Excelsior, but when the Utility appeared, Excelsior disappeared! Does this sound familiar?
Meanwhile, in 1934, R A & F Findlay Pty Ltd, 326 Elizabeth St, were selling... Montgomery!!! This continued into 1935, but seems to have disappeared by 1936, by which time Findlay and O'Connor began selling the Utility JAP.
It is tempting to imagine that the Utility Villiers bikes were Excelsior, and the Utilty JAP bikes Montgomery, but who knows.
Oh, let's not forget Utility Motor Cycle Pty Ltd. In 1933 they listed THREE addresses: 319 Swanston St, and 354 and 417 Swanston St. Perhaps one of these was a factory? 417 Elizabeth St was taken over by Allparts in 1935. During 1935, Jack Taggart advertised - in very modest line adverts - new Utility motorcycles from 319 Swanston St, while Findlay and O'Connor continued to advertise Utility Villiers and Utility JAP in large display adverts.
Les and Wilf Darby - mentioned in the fist edition of A to Z - were well-known racing motorcyclists. At the end of the 1930s, Les was almost unbeatable in local events on his Utility JAP; in 1935 both were racing Sunbeams at a time when Findlay and O'Connor were the Sunbeam agents. They may have been employees of Findlay and O'Connor, but I can't see them as running the show. Les was only 32 when he was killed in a motorcycle race in 1941.
In summary, I have no idea what was going on, except to say that some Utility motorcycles may have been assembled early on (say 1934), but from then on it was possibly the Waratah rebadging thing repeated in Melbourne. Thus "Utility Made in England" tank transfers.
99% of Australian motorcycle manufacturers gave up before 1925, so the 1930s is not really the heyday of the local industry.
Cheers
Leon