20 is not excessive at all. When I have used wipe-on poly, my minimum is 24, and I have generally gone 24-28. Many here and other places will go up to 50. I have used the same amount with Tru Oil also.Two more wipe on poly coats today for a total of 5, and may get a third in later tonight. I'm trying to only put on light coats, and looking at likely having to do around 20 or so coats, which might be excessive.
I try to keep a running tally of my coats on paper but sometimes forget to right it down, so I go with a "when in doubt, do another coat" philosophy. This assures me of my minimum but likely puts me over. Which is not a bad thing IMO.
What wipe-on are you using? Did you mix your own?