No, it isn't -- that's one of the few things I'm sure of. There are MULTIPLE requirements for the final star --.these include All Gold Flags, All Star Coins, and all levels with Mario and Luigi
I checked this by copying my save which had 3 incomplete levels -- one, onebeaten only by Luigi, and onewith 2/3 star coins.without a Gold Flag
Finishing the Star Coin collection (all the standard levels and some other total requirement?) grants one star.
Completing BOTH of the second objectives (and the Star Coins) results in the final star.
I think the confusion is coming as at least one (or more) save file stars require -multiple- objectives to be complete, and folks are assuming the last objective they completed is the trigger...
Can't be sure exactly, other than that I have FIVE STARS and they are shining.
This is what I did:
Finished the 8 Worlds with Mario, during that run, I got all the Star Coins and hit Gold Flags on every level, once I had the credits, I came out with 2 Stars on my save file.
Next, I did the Special World with Mario, had all Star Coins and every Gold Flag.
Luigi runs were next, I blasted through both sets of Worlds and hit the Gold Flags just to be sure.
After I did the final Castle in World S8 with Luigi, I came out and had 5 stars, sparkling and level S Crown unlocked.
The end.
Next, I did the Special World with Mario, had all Star Coins and every Gold Flag.
Luigi runs were next, I blasted through both sets of Worlds and hit the Gold Flags just to be sure.
After I did the final Castle in World S8 with Luigi, I came out and had 5 stars, sparkling and level S Crown unlocked.
The end.