The Chasam Sofer in the Teshuvos (CH. M. 50) writes that he knows for a fact* that his Rebbe R.Nosson Adler had his Pruzbal written only at the end of Shemitta (7th year) and not at the end of the 6th year.
There is a Machlokes Haposkim when to write the Pruzbel. The Itur, Rosh and the Tur hold to write it at the end of the 6th year .The Rambam and all other Rishonim hold to write it at the end of the 7th year.The Mechaber in Shulchan Aruch Paskens like the Rambam to write it at the end of the 7th year.
The Chasam Sofer defends the Mechaber, and writes,Meikar Hadin there is no reason to be Machmir to write it also at the end of the 6th year.
It is very interesting, in Teshuvas O.Ch. 15, The Chasam Sofer knocks the
Chasidim who are Machmir not to wear wool clothing. Why don’t they pick other
Chumros like not eating Chodosh in Chutz La’aretz or to be Machmir to write a
Pruzbal also at the end of the 6th year.
The Ch.S. writes he followed his Rebbe all the time, his hands
did not move away from his Rebbes hands, mammash , he
did so, that he should know all his ways