If you have multiple links between the the same pair of nodes, only the first one is used:
https://go.documentation.sas.com/?docsetId=procgralg&docsetTarget=procgralg_optgraph_details01.htm&d...
The log displays a warning in that case:
WARNING: Link (A,B) in observation 2 of the DATA_LINKS= data set is a duplicate and is ignored.
In the next release of PROC NETWORK (the SAS Viya counterpart to PROC OPTGRAPH), multiple links are handled directly in the algorithm.