Tosfos brings down Rav Chaim Cohen who explains that the reason we can't learn neter reva out from the g"s by maaser sheni is because then we would only know that pidyon applies in years 1,2,4,5 but not in 3 and 6. What is Rav Chaim Cohen's, svara the reason there's no pidyon is because there is no maaser sheni but if there was maaser sheni then there would be pidyon so we still should be able to learn it out from maaser sheni?
Yitzi Loewy, USA
Dear Yitzi
Hello there and thanks for your question. I think that Tosfos means to say that in the years three and six respectively, Revai would not be Kodesh just as there is no obligation to separate Ma'aser Sheni during those years and thus there is no need to redeem it before eating it.
All the best.
Y. Landy