Hi Jay,
It depends if the orders are fixed, firmed or no!
Fix - check in the product master, tab SNP2 if you have Supply Profile maintained and if the option Fix Production or Fix Stock Transfer is selected.
From SAP help:
SNP Optimizer
If you set this indicator, all SNP planned orders from previous planning runs
that are outside of the planning horizon specified for background processing,
are considered as fixed during the SNP optimization run and, therefore, are not
deleted.
If you do not set this indicator, all SNP planned orders from previous
planning runs that fall within the planning buckets profile specified for the
planning book are deleted during the SNP optimization run. In this instance, the
SNP production horizon is an exception: If you have specified in the SNP
optimizer profile that you want the optimizer to take the SNP production horizon
into account, no SNP planned orders are deleted in this horizon.
Firmed - if the orders are firmed the heuristic will not delete them.
Also, in the optimization profile, tab Integration, section Existing Orders you have the possibility to delete or no the orders.
To delete the old stuff it's a good practice. So, I would reply you yes. You can create a job in background to delete all old stuff each night (for SNP use t.code /SAPAPO/RLCDEL, for PPDS use program /SAPAPO/DELETE_PP_ORDER ).
Thanks,
Regards, Marius