Found this on why it's gold rings not golden rings.
Is there a musical reason? Maybe, but read on.
Let's start by looking at the history of the lyrics
The earliest version attested by the Oxford Dictionary of Nursery Rhymes dates from the 17th Century, and gives 'Five gold rings.'
If we step forward to the 19th Century, there are 9 printed documents that contain lyrics, from Halliwell's 1842 'The Nursery Rhymes of England' through to Cole's article in volume xiii of the 1900 'The Journal of American Folklore.'
All 9 of these documents attest 'gold' rather than 'golden.'
I've not been able to find anything before the 20th Century that says 'golden.'
However, if we move to the Scottish version, which doesn't quite have the same countdown, there is a reference to 'goldspinks', which was a local version of 'goldfinch', as in the bird. This makes quite a lot of sense, in that from seven downwards, we have birds:
Seven swans (a-swimming)
Six geese (a-laying)
Five gold-spinks
Four Colly birds [1]
Three French hens
Two turtle doves
And a partridge in a pear tree [2]
[1] A Colley bird is a traditional word for a blackbird. The 19th Century sources are all over the place here. From Canary birds to Colley birds, to Coloured birds. 'Calling birds' is very much 20th Century.
[2] Sources as early as 1867 claim that pear tree is a corruption of 'perdrix' the French for Patridge, and the original may have been 'a partridge, une perdrix' (remember that perdrix is sort of pronounced pear-dree.)
So, for that reason, goldenspinks would be wrong, and goldspinks correct.
Now let's turn to the musical issue.
The song's 17th Century, right?
Well, the version you are probably singing to yourself is almost certainly the 1909 Novello arrangement by Frederic Austin, which is the first written version of the 2-bar 'five gold rings' motif that breaks the rhythm of the previous lines. (The other 'innovation' it added was the written substitution of 'calling birds' for the traditional 'Colley birds.')
It breaks the rhythm - and it's traditional to have a massive ritenuendo on that phrase before the 'a tempo' finish, so I think that it makes a lot of sense to make the syllable last two notes rather than trying to squeeze an extra 'en' in.
So, is it gold or golden?
Since we documentary evidence of when the prolonged 'go-old' melody was written, and can see that 'gold' were the lyrics selected, we can say that 'golden' is a modern travesty. Gold rings it is.
Further reading:
The Twelve Days of Christmas (song)