I have a few random thoughts here.
It’s not uncommon to see variations in a flatware pattern, such that it doesn’t exactly match the illustrations in the pattern reference books (or the original design patent, if it exists) and sometimes a pattern has escaped documentation altogether. Especially for those used by smaller producers, or which were short-lived. There are a number of possible reasons for deviations.
As
@AU Seeker says, one reason may be that the pattern was plagiarised. Even when not protected by a design patent, it would be smart for a copyist to introduce some variations to avoid a potential lawsuit.
It’s also not uncommon for a long-lived pattern to undergo various ‘refreshments’ during its lifetime, with minor improvements being made. This can be for aesthetic reasons, or to improve the crispness of detail, or to reduce the incidence of things like casting flaws.
Pattern books tend to show the pattern as applied to standard spoons and forks. Although not the case here, it’s not uncommon to see variations in other pieces from a flatware series such as knives, serving utensils etc where the pattern is adapted to better suit the size and geometry of the handles.
Patterns were also not necessarily exclusive to one manufacturer and may have variations between the manufacturers who were licensed to use them. That’s particularly the case for designs used by companies who later became part of the International Silver Company (formed in 1892, but continued adding small companies to its portfolio thereafter). The company acquired patterns from the companies it absorbed, including reassignment of patent rights and these patterns then became potentially available to the multitude of manufacturers within ISC.
The ‘Elgin’ pattern was designed in 1883 by Albert Adolphus Sperry, and is documented as having been used by both the American Sterling Co. and the Standard Silver(ware) Co. Despite the use of the words “Sterling” or “Silver” in the company names, this was just a marketing ploy and neither company actually made flatware in solid silver.
Sperry was born in 1831 and died in 1911, working between 1871-1898 within the Simpson Nickel Silver Co. who manufactured base metal flatware blanks principally for Simpson, Hall & Miller but it’s not documented that they were supplied with ‘Elgin’ blanks. It's also possible that you have an earlier version of Sperry's 1883 design produced for someone else.
The American Sterling Co. (of Naubuc, CT) was the successor to the Curtisville Mfg. Co. in 1871 but was bought by James B. Williams and William Williams in 1880 and changed name to the Williams Bros. Mfg Co.
The Standard Silver Co. (of Toronto, Canada) was the successor to the Acme Silver Co. in 1893/4 but merged to the International Silver Co. on an unclear date (possibly 1912).
Simpson, Hall & Miller (of Wallingford, CT) also became part of the International Silver Company in 1898 but continued to operate with the Simpson, Hall, Miller & Co. branding within ISC.
It’s a shame the branding cannot be deciphered, but there are a number of possibilities, with consequent possible dates.