Fall of Gondolin is not canon.
Short answer: yes.
Long answer: It's flatly stated in Tolkien's notes on the matter, and borne up by Lord of the Rings and the final Silmarillion.
Fall of Gondolin is not canon.
I'm just going to repeat that for fun, because honestly, I love bringing it up as well - Glorfindel going all Michael Strogoff on a Balrog is a hilariously awesome scene, as is Ecthelion using his giant spiked helmet to impale Gothmog after it busts both his arms.
Buuuut...non-canon. ^_^
The fight is also noted in the appendices in the timeline, and said timeline and vague description dovetails nicely with what Gandalf says (starts January 15, 3019 for those interested). It does not, for example, say 'Gandalf kills the Balrog in an hour-long fight, then takes a breather for a week while making up a great story to tell everyone.' ^_^
...it also notes that Gandalf fought the Balrog -- including stair-running time, presumably without breaks -- for TEN DAYS.