About Blastoise’s shell/cannons design? Why the change in official artwork and are there any other inconsistencies in other Kanto and Johto pokemon/ starters?

Im a massive fan of this BIG BLUE MANSTOISE, easily in my big 3.

But I noticed this inconsistency with the way his cannon (covers?) are drawn.

At first the design of his shell cannon covers were sort of latch/ trap door shaped, in the TCG he would be drawn this way until in 2002 the first ever appearance (from what Im aware) of his no longer latch cannon shell covers but this more boxy shape.

Then in the very next set he would get his latch back but it would be the last ever appearance of his latch in the TCG.

In the games the time line is more simple, his shell design would stay latchy until gen. His shell design would forever have these 2 boxy openings..

Why the change? I love both but why this change in design; if anyone knows. I loved his very first artwork for the cover of blue version. Its his most iconic imo especially because it was used in base set.

This is also reminiscent of zard having seemingly only 1 horn in early artwork but later definitively having 2.