It's like their the exact oppositesHere's what envelopes look like during normal animation, dark blue colored line, but thin, has slight dimension to it:
View attachment 12784
Here's what envelopes look like in markerbob, very bold grey lines, huge and flat:
View attachment 12785
Like I've said before, I love how normal animation has bold black lines, but thin everything else, but markerbob is the other way around. Normal animation is basically markerbob in reverse.
maybe early season 4 episodes were produced a while before they aired, most season 3 markerbob was made in 2002, thats probably why spongebob looks like he's from 2007 episode