Wow, very enlightening! So cool. Well, at least we know for sure that the filming suit at least
started with 4 toes.
The 3 toed Godzilla in the promo photos with the actors earlier up the page definitely appears to be a suit. Holes in the neck, wrinkles in the tail, on the legs, at the waist (not to mention the photo of him holding an umbrella HAS to be a suit...). The question is whether it’s the actual filming suit or a specially made promo suit. I’m leaning toward it being the actual filming suit with a toe lopped off. The details just match the filming suit too well and it’s well known Toho used the actual filming suits for promotions until the 70’s when they started making cheaper suits specifically for public appearances.
Here’s the GTTHM suit doing a promo in front of an audience:

And here’s the three toed suit holding the umbrella:

So, in my mind, the only real questions left are when were the toes removed? And why? My guess fort he latter, like others have stated, was for mobility issues (make it easier to walk), or maybe the toes got damaged. As for when? Who knows, we may never figure that out.