I too, believe that a 100-200 foot snake is not very likely due to most of the reasons posted here.
But... could it be possible, that the Anaconda for example, has been diminishing in size rather than growing?
I could speculate that 200+ years ago, food sources for snakes may have been in abundance, wherein they may not have needed to exert much energy to
feed.
We could possibly be on the downside of the evolution of the snake whereas they have come to adapt to their current environment. Thus, becoming
smaller due to food availability.
Early recorded accounts of large snakes, such as mentioned in this post, could be posed as feasible.
Hmmmmm....