If you compare his clothes in "Donkey Kong" artworks with his clothes in "Mario Bros." artworks, he didn't have a brand image yet.
In fact, in the pre-"Super Mario Bros." artworks, even the character himself looked completely different. SMB was literally the first time that Mario had his typical look.
And it wasn't until the second game (the Japanese SMB2, "The Lost Levels") that anybody besides Mario had their typical look: Bowser and the Princess didn't look like Bowser and the Princess in the SMB1 artwork yet, and the Koopa Troopers were drawn in a strange style. Only in SMB2 (J) was their design standardized:
https://assets.catawiki.nl/assets/2020/ ... 9a1db4.jpg
And even there, they hadn't established yet that the Princess is taller than Mario. This and Luigi's canon artworks weren't defined until SMB2 (USA).
(Although it was brought to my attention that Luigi's modern design was first used in the box art of "Famicom Grand Prix II" which predates SMB2 (USA) by a few months. But I assume the design was probably still established because of SMB2 and the two games were simply in development at the same time, so the car racing game already used the new Luigi design.)