The stars of the Order have indeed been made in a great variety of shapes. Even though metallic stars have been worn for a long time, it wasn't until the late 1810-20s that the old embroidered stars fell into disuse. Even so, until the 1850s, the official stars (provided by the Queen) were still embroidered.
These years of experimentation resulted in a great variety of different (metallic) stars being made, at the expense of the Knights.

The Garter Jewels of the Earls Spencer show a number of different stars.

https://www.christies.com/lotfinder/Lot/the-unique-spencer-family-garter-jewels-from-5335281-details.aspx

In Queen Victoria's reign, an attempt was made to standardize the stars, and the pattern that was adopted was in use until the end of the 19th century.
Ii was gradually replaced by another one, which is still worn today.

A star in the Victorian pattern, which had eight points of equal lenght



Until the 1930s and possibly later, Knights of the Garter were asked to return the star of the Victorian pattern in exchange for the new one.

The (curent official pattern) Star of the Earl of Halifax in 1945:



Strangely, King Wilhelm Alexander of the Netherlands was presented with a star in the Victorian pattern during his recent State Visit.

Lord Mountbatten wore a jewelled Star fashioned after the current pattern, which is distinctly more elongated than the Victorian pattern.

The Earl Mountbatten of Burma by Allan Warren (1 January 1976)




Bern Schwartz, Louis Mountbatten, Earl Mountbatten of Burma At Broadlands, December 1977




Lord Mountbatten at Broadlands, by Andrew Newman spring of 1978 'The Great British' (published in 1979 by Sunday Times & NPG)