I've heard over the years nandrolone metabolites can present in the body 6-12 months after cessation making user prone to failing drug tests..
The same has been stated with regards metabolites and recovery, ie: HPTA takes longer to recover from nandrolone..
I don't know where the hypothesis of nandrolones long lasting HPTA suppression originated, but I found this from Nandi back in 2004:
I've never believed that long lasting nandrolone metabolites had anything to do with slowed recovery. This is evident from comparing figures 1 and 3 in the often cited study by Minto et al
After a single deca injection testosterone returns to normal as plasma nandrolone levels drop to zero over the course of a month. If there were long lasting nandrolone metabolites contributing to suppression, testosterone would still be suppressed after plasma nandrolone returned to zero, which is not the case.