my two cents,
What is the ideaof having differentretentionsin a session?
Ifat the end ofthetapecanbe reuseduntil itexpiresultimate protection!
If you havemany tapescan do that,but ifyouhavelittlesoon befinished,becauseafter putting52 weeks ofprotectionuntiltheprotectionexpiresthe tape can beused againand evenyou want to usepermanent protection, then allincrementalsare dueand that isspace that is notusable untilyou formatthe tapeagain.
I were youdotwo specifications, one forincrementaland othermonthlyforpermanent protection.
Sotheincrementalexpirein 4 weeks andre-usesthat tape.
If you putthemonthlybackuppermanent protectionbetterleave allthat specificationas permanent,yourspecificationmakes no senseas well asyou put it.
regards