This does NOT work for me.
I am using iTunes 12.6 -- on Mac OS 10.12.
With Podcasts selected on the "left-column" menu, I get three options at the top-middle (below the apple in the Mac iTunes app): (1) LIbrary (2) Unplayed (3) Store
Selecting a podcast does NOT change that menu.
When I select a podcast -- I see the podcast window on the right-half of the screen. The little cogwheel seems like it would allow me to "limit episodes" but it is unclear whether setting that to "off" turns off the limits (making the number of episodes "unlimited" or sets the limits to "no-episodes".
Although I seem to be able to click the blue ball w/the 3 white dots and unsubscribe -- this leaves me with 21 episodes for that podcast shown on the "column menu" in the middle of the iTunes Library screen.
I have gone back and forth from the Mac iTunes to my iPhone 6 iTunes for about the last two hours. Nothing but frustration.