Corrected entry: In the bedroom scene with young Reggie conducting the orchestra, his pajama top has an open neck then the next shot he has a bow tie on.
Corrected entry: Elton opens a screw capped bottle of wine in one scene with a flourish. These were not introduced until the mid 80's and then only in New Zealand and Australia.
Correction: Screwtops started to appear on wine about 1976 (although not widely). Elton John could have gotten hold of a screwtop wine bottle from any country using them, because wine can be exported. Screwtops for wine bottles were developed several times in the 20th century, starting to be successful in the 1960s and being sold more widely in the 1970s. Nowhere near as popular as corks at the time but not impossible to find for a flamboyant and rich pop star. They were sold in Switzerland, the US and UK as well as Australia and New Zealand. Of course all that is irrelevant if the prop bottle is indeed from a later time but unless that can be seen without pausing, this is not a mistake.
Correction: Reggie's pyjamas changing into having a bowtie and his dressing gown turning into a black jacket is creative cinema, because is Reggie imaging/dreaming of conducting an orchestra. Not a movie mistake.